I reckon Anne Heche was just an attention seeker, she got with Ellen right as Ellen was about to come out and they became the most famous lesbian couple at the time (not that hard then really) and Anne just wanted that fame. Did she have any girlfriends before Ellen? I'm pretty sure she hasn't had any since because it wasn't long after she denounced it all.
Looking at her wikipedia page I think she probably just wanted someone to love her and thought Ellen would be the best as she doesn't seem to have a good relationship with men.
So I agree she wasn't ever gay or even bi.