That was 10 years ago before she was able to finally convince her former boss she did not need to work full-time to do her job, long before she joined NAB.
"Discussions about my return to work, part-time, after maternity leave didn't go so well," she says in a new book The World We See by Sarah Liu, to be released next month.
"I was told that despite being capable of doing the role, it wasn't possible to do it part-time. I was told that no one in the industry had ever done that job part-time so... the answer was no. Those anchors of fairness and inclusiveness got a giant jolt.
"After a challenging and fact-based conversation (I was red in the face and swearing on the inside) it was agreed that I could, in fact, do the role part-time and I went on successfully until I had our second child."
Collins, who is now a business manager at NAB, returned to full-time work last year, but says she will not stop working flexibly. She said working part-time forced her to understand her priorities, personally and professionally.
"NAB is very supportive of flexible working. I came across for that reason and they promoted me while I was part-time," she told Fairfax Media.
Marian Baird, Professor of Gender and Employment Relations at the University of Sydney said many women in the corporate sector in senior management jobs struggle to convince their bosses they can do permanent jobs part-time. She says Collins is among rare exceptions.
"It is a massive sticking point in organisations to justify and make it work," she said. "The struggle is can you get management jobs at part-time hours."
Professor Baird said women at different ends of the labour market were struggling to balance work and family.
Permanency can give women in the corporate sector "a place to make an argument from which is much stronger than if you are casual and you want to be made permanent at the same hours".
"We need to recognise at the top end of the market some people will need to do senior jobs in a part-time capacity and the lower end of the market, we need to be able to offer security of work," she said. "And for both ends that's about balancing work and family in a society that we all want to live in."
Many long-term casuals are also fighting for the opportunity to make their jobs permanent for greater security and predictability of employment.
"It is not just about retail workers and shop assistants. It is about teachers and care workers and being able to provide better ongoing guarantees of work is a very significant social issue," Professor Baird said.
The ACTU is running a case to help long-term casuals get permanent positions as part of the Fair Work Commission's four-yearly review of modern awards.
Its submission to the review says growing casualisation of the workforce has a disproportionate impact on women and contributes to the gender pay gap and inequality.
"Mothers who desire part-time work for flexibility purposes generally prefer permanent part-time work more than casual employment and the insecurity of casual employment contributes to the 'motherhood gap'," the submission says.
"Female casual employees experience ten times the chance of unwanted sexual advances in the workplace compared to women employed on a permanent basis."
Sonia Pomida, from Prestons near Liverpool, is among workers taking industrial action this week against what they fear is the casualisation of their workforce at light manufacturing company, Thorn Lighting in western Sydney.
She was employed as a casual for about six months before her position was made permanent about 18 years ago.
"There are more benefits like annual leave and sick leave being a permanent employee," she said.
"The company wants to bring in casuals to do our jobs. That's why we are on strike."
The Australian Manufacturing Workers is negotiating a new enterprise bargaining agreement for workers at Thorn Lighting and is demanding that casual labour hire workers are paid the same rate as permanent employees.
The union says workers are concerned that increased casualisation of their workforce is a threat to job security and that the use of labour hire staff will undermine hard-won pay and conditions.
Fairfax Media contacted Thorn Lighting but it declined to comment.
Written by Anna Patty for the Sydney Morning Herald