The finance secretary, who has been on maternity leave and away from frontline politics since early summer last year, made the admission as she launched her bid to replace Nicola Sturgeon as SNP leader, widening the race to include three candidates to become the next first minister.
Ms Forbes told BBC Scotland she had “significant concerns” about gender self-identification. The UK Government has blocked the Gender Recognition Reform Bill from becoming law, despite it passing a vote in the Scottish Parliament.
Ms Forbes said: “I understand the principle here, which is that the UK Government should not overturn Scottish legislation. That is an important principle which I hold to.
“But I think on this, seek legal advice and recognise it is not a priority right now for the people of Scotland, who are focused on other things.”
The MSP for Skye, Lochaber and Badenoch is considered the frontrunner for the job among members and is set to face off against health secretary Humza Yousaf in the battle for Bute House.
She also joins outsider and gender rebel, Ash Regan, who announced her candidacy on Sunday, as did Mr Yousaf.
Angus Robertson, the constitution secretary, is viewed as another potential successor but ruled himself out earlier on Monday.
Announcing her candidacy, Ms Forbes said she wanted to “unite the party and the Yes movement”.
She said: “The nation and the Yes movement are at a major crossroads. The choices we make in the next few weeks will have a profound impact on our future and our children’s future
“I cannot sit back and watch our nation thwarted on the road to self-determination. Our small, independent neighbours enjoy wealthier, fairer, and greener societies – and so can we.
“We urgently need to unleash the full talent of the SNP, the wider Yes movement and the country at large. We need to choose strong, competent leadership to deliver independence – the leadership that I can offer.”
The finance secretary added: “I believe we need somebody who can unite the party and the Yes movement. I will reach out and listen so that every member feels valued and able to contribute. That is important within the party, but it is also important if we are to persuade others of the merits of independence.
“We need a leader who is bold and brave and energised, who inspires confidence from the SNP membership and who inspires the confidence of the people of Scotland. From the youngest to the oldest, regardless of where you live or who you are. We need somebody who voters can trust, who has integrity and commitment. I am that leader – and I want to lead the party into better days.”
Ms Forbes was thrust into the limelight following the resignation of the then-finance secretary, Derek Mackay, forced to quit in disgrace in 2020 over text messages he sent to a 16-year-old boy.
The then-29 year old delivered the budget with less than a day’s notice, becoming the first woman to do so.
Ivan McKee, understood to be leading her campaign on the ground, told BBC Good Morning Scotland that the MSP was a “hugely talented individual”.
He said: “I think Kate is a hugely talented individual, I’ve had the pleasure of working with her over the past seven years and seen first-hand what she is able to deliver, her focus on the things that are important to Scotland and her ability to engage with people on a very real and authentic level and persuade them of her case.
“And I think those talents, to be able to deliver excellent public services, a strong economy, a green economy for Scotland and to be able to persuade people of the case for the SNP and for independence, are exactly the assets we need in a leader.”
Candidates have until Friday to secure 100 nominations from at least 20 local branches to secure their place on the ballot, with the new SNP leader being announced on March 27.