It wasn't until Ms Allen "became pregnant that she felt it was time for a complete change, because she had "seen over many years" how pregnant women and mums who returned to work were treated.
"I think mums in general get sidelined after they have children," she said. "A lot of employers, when an employee has a child they think they suddenly lose their brain. It's not the case at all, they just have different priorities.
"It's really hard for a woman after they've had a child, if they've had a successful career, to return. For me, I thought, 'This is my chance.'"
Ms Allen, who has just released a book titled The Busy Mum's Guide to Weight Loss, said she was surprised when she started gaining weight. "I was like, 'Holy moly, this is a new thing'," she said.
"I started looking into weight gain in pregnancy and uncovered this new thing for me, how much people gain weight in pregnancy and how difficult it was for women to lose weight after they have children."
Finding that most of the solutions were "mass market, fad diets not based around good nutrition", she saw an opportunity for a "healthy, supportive, community-based" weight loss program. "I talked to my husband, we sold our house and rented," she said.
"I quit my job at six months pregnant. I just believed in it so much. I invested $300,000 into the business, I just threw everything at it. It was all about doing something I loved. I thought, the worst thing that could happen is I could go back to my old career, the best was that it was going to resonate with women all over the country."
It wasn't easy going at first, however. The Healthy Mummy, an e-commerce business that offers a subscription-based weight-loss program and sells its own range of health products and merchandise, took three years to turn a profit.
The money left over from selling their house kept them going during that time. "After three years it was like, hooray," she said. "I had no idea that would be the case, I was going in blind. I had never run a business before, didn't have a clue about that type of stuff.
"It's all a bit scary [looking back] now, I'm a typical entrepreneur that has a vision but doesn't have a clue about finance. On year two we got a finance person in, that helped. But ever since year three the profitability has been crazy."
For the past three years, The Healthy Mummy has had 100 per cent year-on-year revenue growth and is on track to reach $22 million this year after $10 million last financial year. The company has just launched in the UK and is aiming for the US in 2019.
Ms Allen said her most important advice to anyone thinking of starting their own business was to "always place the customer as number one". "If you don't worship the customer, your business will fail," she said.
And if you're not "110 per cent committed" to running the business, maybe consider working for someone else. "You can't just dip in and dip out," she said.
"Whatever your business is, you have to have a complete passion for it, because if you can't be passionate about it, it will soon fade. I'm as passionate today eight years later as I was when I started."
And they finally have their own house again. "It took me seven years — we just reinvested all the money into the business all that time — but in September I actually bought a house in Seaforth [north of Sydney]," she said.
"We now have two small kids, so we need a bit more space."
