Willow wondered if she was now an official lesbian,. I like how she just jumps into the "official lesbian" idea. Showing her jumping to lesbian, without thinking of bi, doesn't actively explain why Willow never thinks of herself as bi, but it supports her self-identification as a lesbian in a way that does not require an explanation.

I'm not sure if that made sense. The tv series always left me wondering why Willow didn't consider herself bi. With your story, I'm satisfied that she identifies as a lesbian.