Honesty people. It would make things a lot easier.
It seems weird that she's hiding it in the first place even if she doesn't 'confess' her feelings right away (unless it's some psych messed up backstory where she somehow ended up obsessively stalking her and learning every small detail about her without anyone knowing and deliberately planned to go to the same school, even if the classroom assignments should be random or so)
If anything it'd be a chance/opportunity to have more 'charm/charisma' and say something cheesy like "no way, that was you? Wow, small world/it must be fate!" as opposed to wanting a 'blank slate' (which, the long hair girl fell in love at first site anyways regardless of the flashback)
(wait who's that person at the end, is it the childhood friend with longer hair?)