Mrs Maher, a Dubliner, would fit nicely in a James Joyce novel. Tall and strongly built, she now lives in Ocean Grove. She is married to Nathan, a builder, and they have two boys. She will make you a cuppa and talk your ear off for hours. She will happily discuss baby poo and how crazily her breasts inflated when she was breastfeeding. But Mrs Maher's manner belies the terrible sadness she and her husband have endured: after 17 pregnancies they have only brought two babies home.

Then there is Mrs Maher's alter ego, Tizzie Hall. This other woman is a business powerhouse and best-selling author who is building a home that piqued the interest of Grand Designs. Cyclist Cadel Evans is the godfather to her eldest son. She is an international brand, adored and reviled by new parents with equal passion in the emotive, profitable world of baby-rearing. The number-plate on her station wagon says it all: TIZZIE.

The self-titled "international baby whisperer" specialises in getting babies who don't sleep well into a regular rhythm of feeding and sleeping – even those with medical issues such as allergies or reflux.

Her strict rules involve fixed feed and sleep times according to the baby's age.

A two-month-old, for instance, should be woken at seven and fed. At 8.45, the baby should be swaddled and put to bed. At 11, she should be woken and fed again. And so on. Hall stipulates what clothes and bedding should be used and her tone is firm. "You will wake and feed her [at 7] even if she last fed at 5.30am," she commands the weary mother.

Sleep, or lack of it, is an obsession for new parents: who's getting it, who's not, why not.

One mother I know had a baby that would only sleep for 20 minutes at a time unless he was upright on her chest. After weeks of this, she was a physical and emotional wreck.

Resolving cases such as these is at the heart of Hall's multimillion-dollar business.

Since releasing her first book Save Our Sleep in 2006, she has written two others (on feeding and toddlers), and built up a booming online shop with her own brand of products as well as a physical shop in Ocean Grove.

Save Our Sleep has sold more than 100,000 copies. She runs an online forum for paid members and employs a 12-member "team".

Hall's passion for babies can be traced back 33 years to the death of her brother, Richard, from sudden infant death syndrome. He was eight weeks old and Hall was seven; the only photo remaining of the boy shows him in her arms. After his death Hall went house to house, asking neighbours if she could hold their babies; a poignant trigger, it would seem, for her future career.

Teenage babysitting jobs morphed into childcare roles in London, where she developed a knack for getting babies to sleep. Then Hall took on a job caring for three children, from newborn until school age, while their parents worked overseas.

The couple decided to move to Australia in 2002 and Hall came ahead of them to settle the children. It was then that she and Nathan got together – "after I hired him to come and change all the electrical plugs".

A weekly column in Practical Parenting magazine followed, catching the eye of Alexandra Craig, an editor with Pan Macmillan, and the Tizzie brand was born.

Craig says: "There was nothing else Tizzie was going to do with her life . . . She lives and breathes babies and children."

Hall's guiding principle is establishing a routine for babies. It's not something she invented, she says, but reflects the natural patterns of a child that is warm, well-fed and given a safe sleeping environment. This, she argues, enables parents to be able to tell the difference between a hungry cry and a tired cry and respond accordingly.

Hall says she has never encountered a child whose sleep problems have not been resolved using her methods – with the caveat that every step of her strict routine must be implemented.

"You have to do it exactly my way. You have to follow the routine, you have to follow the bedding. You have to follow the feeding," she says.

Is this not too direct, too bossy? Hall smiles and replies: "That is one of the reasons why people love it. So many people come to me and go: 'I love the fact you're that exact.' That's why it's so successful."

She says that in addition to the thousands of grateful parents who contact her every year, all the women in her mother's groups have excellent sleepers – because they've taken her advice.

Elisha Crook, a member of Hall's first mothers' group, says: "Of the six of us, five have used her book to the letter. All of us have two or three children who all sleep 12 hours overnight and have no sleep issues. The one who doesn't follow it has had, well, issues."

Tizzie's disciples are vociferous and describe her, sincerely, as a life-saver. One contributor to her Facebook fan site, Di Craig, writes, "The [Save Our Sleep] book literally saved our sanity. Hubby and I had no idea we had to teach our bub to sleep and were having a terrible time with her awake till 12 every night. We heard about the book from a friend when dear daughter was six weeks. Bought it that day and started using it. Love it."

But Hall's opponents are equally firm in their opinions. The partner of one mother who tried Hall's approach said he "hates Tizzie's guts. I blame her for [his partner's] post-natal depression. She nearly went insane trying to put those routines in place."

Hall has been targeted, too, in online hate campaigns. Most prominent is the Tizzie Hall Didn't Save Our Sleep Facebook page, which has more than 1700 supporters. Contributors denounce her as "the evil one", and describe her as unqualified and uncaring. The Age twice attempted to contact the facilitators of this page but received no response.

Liz Price, an experienced midwife and lactation consultant, manages the breastfeeding clinic at a big maternity hospital in Melbourne. She is scathing about Hall's ubiquity, the influence she has over new mothers, and the pressure she says Hall puts on parents to try to fit their babies into a one-size-fits-all model.

Like a number of Hall's critics, including many on the Facebook page, Price admits that she hasn't read Save Our Sleep cover to cover. "I read the preface and the routines and I was so angry I couldn't read any more."

But she says she deals with many women who have tried to apply Hall's methods to their babies' feeding and sleeping patterns and, when they have failed to get their babies to sleep through the night, feel an overwhelming sense of failure. "You wouldn't believe the calls I get, and I can tell when they've been using that book."

Price voices concerns, echoed by many others, about Hall's apparent lack of qualifications.

Hall won't be drawn on what her qualifications are, saying the proof is in her experience and results; that her publishers know what she's done, and that the book has been approved by paediatric experts, an assertion Craig supports.

"I don't see why I should talk about qualifications," Hall says.

"I'm not looking for more business."

But Price's main beef is with Hall's strict rules on feeding.

"She doesn't differentiate between babies, and every baby is quite different. Each mum can have different problems, such as low milk supply or sore nipples, which can all affect the way a baby feeds," Price says.

"But [according to Hall] if your baby doesn't fall into doing it her way these women read it that they are not being a good mother, even being a failure."

Price says Hall's methods don't allow for the "normality of difference between us as a species", that she places too much emphasis on sleep, when sleeping through the night, particularly in the early months of a baby's life, is "not the norm" – although Hall herself says that not all babies under three months should be expected to sleep through the night.

Price acknowledges that most babies will settle into a three-hourly feeding pattern, as Hall advocates for older babies, but the main problem is with Hall's tone.

Price says her tone is too dogmatic, too hectoring.

"If she changed the way that she comes across and made allowances for mums, then perhaps that would help them understand that they're not a failure dealing with an abnormal child." Price even speculates that the Tizzie Effect has led to an increase in post-natal depression levels.

But other experts support Hall's techniques. The book is commonly recommended by GPs, paediatric nurses, psychologists and midwives, and Patsy Thean, unit manager of Masada, a Melbourne private hospital with a "sleep school" in its mother-baby unit, is cautiously supportive of Hall's methods. She says that establishing a consistent pattern of feeding, playing and sleeping is fundamental for all babies and helps parents to distinguish when a child is hungry or tired.

But, like Price, Thean says that having personal support is key: "Some mothers need more support than others and if you have an unsettled baby the book is not enough."

Hall is philosophical about the criticism directed at her. On one hand, she learnt that if someone hates your brand you're doing a good job of branding. "That changed my life because I went from being upset about the negative stuff to realising that [being controversial drives sales]." Her pet hate, though, is people spreading misinformation about her techniques when they haven't actually read the book.

The poignancy of Hall's success as a self-declared baby whisperer is the difficulty she has had carrying a child of her own. She says that she and Nathan only have to "look at each other" to conceive, but the struggle is in reaching full-term. "Is it worse not being able to get pregnant or is it worse getting pregnant and not being able to get past the third trimester? I don't know," she says.

While some of their losses have been at an early stage, Hall has also endured other complications – one ectopic pregnancy and numerous later-stage losses.

The worst, she says, was her most recent, which followed the ectopic pregnancy. "Everyone has an opinion," she says. "Everyone felt the need to come up and say: 'My friend had an ectopic pregnancy, then they removed the tube, and then went on to have another baby'. When I found out three months later that I was pregnant, I was convinced that I'd had my problems, I had had my tube removed. I thought I was the perfect body to have the baby. But I lost that one."

After coming out of hospital she took her boys, Daragh, 5, and Cillian, 3, out for brunch. As she was contemplating how to break the news to them, a stranger approached and criticised her for allowing the boys to have iPads. "She said: 'You'd think that you of all people should know that screen time is really bad for children.' " recalls Hall.

"And I thought: 'No, you don't know'."

Crook says the most vulnerable she has ever seen Hall was after that loss, but that Hall also gets stressed by not having enough time to spend with her sons because she spends so much time advising strangers on their children – whether online, at conferences or in her shop.

But the baby whisperer, who turns 40 this year, is adamant that she and Nathan will keep trying for another child. "I know we're going to have another baby," she says. "I just picture it. I know it. I feel it."

Julia May is a Melbourne writer.

@juliacmaybe