She probably never was gay, but simply succumbed to peer pressure.
There is an expression on college campuses and from what I can tell applies somewhat more to female athletes. LUG:
Lesbian Until Graduation.
From what I’ve seen/heard, this is the case. Either they think it’s ‘cool’ and the thing to do/claim; or they’re pressured into proclaiming it, whether it’s true or not; or they are harassed because they’re straight.
Your post illustrates the confusion between the idea of “gay” as an integral, even inborn, characteristic of a person, and “gay” as a behavior descriptor, “This person has a sexual attraction for or has sex with people of the same sex.”
Which is it?
You are probably right. Sexuality is imprinted when you are in the womb. It has to do with hormones during gestation. You can be 100% straight or 100% gay or anything in between. Deviant sexuality can also be imprinted by sexual abuse on a young child. They are victims, victims of predators and to be pitied but not condoned. Sometimes they become super predators as adults.