vague meta: femslash

One of the common complaints about boyslash is "you can't just have a straight male wake up gay!" In fact, lots of people tend to like fic where it's all explained. How they're really bi, or they're hiding, or whatever.

So the question becomes, when I'm writing femslash, with a canonically-straight woman (I'm sorry, but if I want to be correct, I don't think any woman is supposed to be lesbian until they wave a little flag) do I need to give context? Do I need to justify their becoming suddenly all about the girlparts of their friends?

Or is it ok that I'm too shallow for that?