I don't think it's a matter of her following him around when that girl chased after him. She clearly saw how troubled he was with her, so she kind of played the guard for him, and as soon as she had the chance to help him, she did.
Although I have to say,
that room scene, at first I thought she was changing and she simply forgot or didn't have time because she heard what was going on. On a side note, I have to say, taking her personality into account, she really is an attractive shy cute girl, she doesn't really overreact to anything like Mio from K-On did, which seriously was pissing me off, making her attractive look simply annoy the hell out of me. In this case, she has nearly everything about herself in control. She even didn't force her feelings on Tetsuro, she said he doesn't have to answer her at all, she is fine if he doesn't like her in a romantic way. She clearly confessed only to let the burden off her chest, and quickly cleared up the atmosphere so in any even even if he doesn't like her like she does like him, they can remain friends without any awkwardness.
That made me like her even more, even if you don't love her, she is still a very pleasant character, a positive part of the story.
She wanted to keep a low profile, which means she didn't try to make friends, this means she has this good aura that just happened to place some people around her that accepted her. Personally, I think she lacks a bit of self confidence, just because she is who she is, doesn't change the fact that who she was until now, without anyone knowing her secret, changing anything about her. She's a nice, good girl. It would be very hard for me to dislike her.
Kana however is starting to piss me off at some points.
