The way I understood it is that Hidari did have a crush on her teacher, but she knew it was never going to happen. She still likes the teacher at the end and that's why didn't answer to natsuki at the end.
This doesn't mean she doesn't "like" natsuki, it's not that strange that she started liking her, she's the only one who read her writings and was in love with her, maybe she sympathised with the fact that Natsuki loved someone that didn't return her love, just like her with the teacher. Yeah it sounds a little weird, but it's plausible.
Honestly my gut feelings goes with this, but I want it to be a happy ending uhhh.. So conflicting uguu