I get that, but at the same time, I see why she'd do it. I mean, she--even fictionally--lives in a society that constantly assumes that she's heterosexual until proven otherwise. At least, I assume this, because that's how our society operates; you have to announce non-heterosexual identity and then even sometimes you are questioned about it (especially with bisexual identity), and especially with women's personal sexual identification there are a lot of men that don't think a woman is being serious when she says "no, I like women" (think about the trope of the creepy guy going, "oh, you're a lesbian couple? do you like threesomes? hurrhurrhurr", because ugh that shit happens). Or worse, completely don't respect her right to make that determination.

It's not necessarily the honest or the best response to insist monosexuality, but it's a defense mechanism and I don't get mad at her for it. (It'd be hypocritical; I did similar things when I was younger, sillier, and far less confident in my ability to assert myself.)