Oh, DiDi (of all people) reminded her of the word years ago, and it’s pretty clear that she has the vocabulary. Insofar as Sonya’s “not a lesbian” fixation makes any sense as more than a tired comedy catchphrase, it’s clear that her issues are emotional, and not something that can be shifted by a mere explanation. You can’t argue someone out of a position with logic if it wasn’t logic got them there in the first place.
Sonya’s confusion should (logically) stop when she accepts that the world is bigger and more nuanced than her old system of categories allow, and that she can be a lesbian — or, as she is, bisexual — and still be her highly feminine, widely liked self, and that conventional respectability doesn’t have to matter to her. Which, actually, Angel might help with, because Angel is a walking lesson in blurred categories and defiance of convention.
“Can be”, not “is always”. And it’s the difference between continuity and stasis.