I can't remember her saying 'scientists' except when she said 'we're not scientists'.
She's right though, It's for the government to define terms and decide on the exact wording of laws and amendments, preferably in consultation with the public and allowing plenty of time for debate and scrutiny.
I know there has been a lot of concern and argument among feminists and women's rights campaigners about exactly how to tackle this and whether campaigning for sex to mean biological sex is shooting ourselves in the foot. TBH I can't quite get my head around all the arguments (beyond #RepealTheGRA which absolutely needs to happen, regardless of amendments to the EA) but I'm not worried, this is still in the very early stages.
There is a very, very long history of common law understanding of sex. Until relatively recently the law treated men and women differently in all sorts of areas, mostly to women's detriment.
Nobody was confused about the meaning of sex, male, female, man or woman when we were denied the right to own and manage our own property, or keep our children in the event of divorce, or when the grounds for divorce were different for men and women, or when we could not vote or stand for parliament because of our sex, or when we could legally be paid less because we were female or when we had different pension rights, or when women couldn't have bank accounts without a man's approval ...
On a more positive note, nobody was confused 200 years ago when Elizabeth Fry's campaigning resulted in the Gaols Act which for the first time separated and safeguarded female prisoners from males. She knew exactly how the prisons should be segregated and so did the government when they passed that law.
If clarification of the EA goes ahead, and I hope it does because I think repealing the GRA is years away and women are suffering now, then I expect the government will consult scientists but ultimately I expect them to defer to the precedent of hundreds of years' worth of common law. Nobody has ever really been confused about the meaning of sex, male, female, man or woman.
We already have birth certificates which are legal documents that record our sex, in accordance with the common law understanding AND in accordance with our biological sex. There's no need to reinvent the wheel. Everyone knows what a woman is.