"I'd managed to get myself to uni and I'd finished a really good engineering degree, but I just kind of fell off the wagon."
Luckily, Penn still had her job in the chemical industry, but on a graduate wage there was "no way" she could afford a place of her own.
Her partner was still living with his parents, which meant she was forced to couch surf or crash with friends as her pregnancy advanced — although she knew the situation could not go on forever.
"The period came when I knew there was nowhere for me to live and I wasn't earning enough money for a deposit for a flat, so my only option was to go to the council and register myself as homeless," she said.
However, at that time, placements for people who were registered as homeless in London were limited and awarded on a first-in, first-served basis, which meant those seeking shelter had to physically queue up in hope of gaining a roof over their heads.
Penn, who was now in the late stages of pregnancy and growing increasingly desperate, spent entire nights outside the council office to ensure she would be first in line the next day.
"It was scary as hell because it wasn't the way my life was meant to go," she said.
"It was flight or fight — I was going into work trying to keep it together, but I was always on edge — it knocked my confidence and made me want to shrink and hide.
"I remember having this big bump, but I didn't want people to ask what was going on."
She was finally given a home just weeks before her daughter Leah was born, which Penn described as "life-changing".
"I finally felt like I had hope. The biggest thing for me was that there was nowhere I could afford to rent, but after I found housing I realised that worst-case scenario, I could do it on my own," she said.
"After I had my daughter I was able to come home and care for her — we had one bedroom but it was such a relief to have somewhere safe to live and I was so grateful."
Penn took just over a year of maternity leave — but was only paid for six weeks.
She also split up with her daughter's father, but somehow, she made it work — and while she cared for her daughter, she often fantasised about starting her own business, although she eventually returned to her original job.
But when the 2011 London Riots swept through the city — and through her housing estate — Penn knew she needed a change.
She ended up meeting a man on an online dating site who was in the US air force and living in Japan, and the couple eventually married, with Penn and her young daughter moving across the world to be with him.
A son, Levi, soon followed, and Penn spent her time in Japan "hustling" — teaching aerobics classes and training as a hairdresser.
But "cracks started to appear", and when a management consulting job came up in Australia, Penn jumped at the chance, moving Down Under when her son was seven months old and her daughter seven years while her husband remained in Japan.
"It was sink or swim — I was in a foreign country with no family and one friend," she said.
Penn and her husband eventually divorced, and after taking on a second job in Australia, "the penny dropped".
"I thought, you've only got one life — do you really want to keep doing this until you reach retirement age'?" she said.
"I had a deep conversation with myself about what I was wiling to risk to give me the future I wanted.
"I decided to open my own consultancy, which at the time was the biggest risk I'd ever taken — it was mental, there was no guarantee of work, I was in debt and then I just decided to quit my stable job that was paying well."
She launched her own engineering consultancy firm, Penny Consulting, in January 2016, and it soon took off, with branches eventually opening in both Sydney and London.
Last year, the 37-year-old also opened a F45 gym in London, and she has also launched another business, W Squared Coaching, a life coaching firm aiming to "empower people to be their best versions of themselves".
Today, she splits her time between London and Sydney, and her three businesses are now turning over more than $A1.6 million per year.
"I still pinch myself," Penn said of her business success.
"It has taken a while, and sometimes that impostor syndrome pops up and I think I must have fluked it, but I'm extremely proud of myself."
Penn also hosts the Did You Get The Memo? Because I F***ing Didn't podcast.
