She didn't change it. She was always bisexual (women aren't as discretely homosexual or heterosexual as men). She just hadn't previously realized it. She always had a choice.
There is the nub of the issue; maybe we ALL have a choice. Just as everyone is a substance abuser, one could say everyone is bisexual. The majority of people choose heterosexuality; the odd minority choose to be something else. Odd also, is how the choice of sexuality ties in strongly with other neuroses such as narcissism, exhibitionism, sadism, masochism, etc.?
***She was always bisexual...***
A bisexual is like the fat woman in a restaurant. When the dessert tray comes around she can’t decide which to choose. So she takes two. In other words, she has no self control.