I'm honestly more curious about what Igarashi came for. Just to see how Chidori's doing, as she did seem to genuinely like the younger girl if nothing else? Try to clear the air between them, as those chocolates suggest certain regrets and the poor terms they parted ways on probably bothering her? Or is she actually insensitive (and/or desperate) enough to want to try and see if she still has a chance, since for whatever reason she apparently started having second thoughts about that rejection quite a while ago already and presumably has no idea Chidori's found someone new? (Mind you she'll probably clue in on what's up with Nanoha within minutes of her entering the room... and then fall hard for her given Nano's oft-demonstrated unsurpassed gay magnetism)
Guess we'll be learning that circa next chapter.
That is a very good question. We’ve seen this “graduated-ex/almost-ex returns to the cultural festival” trope many times before—sometimes it’s just a former school star revisiting the scene of past glories, except in this case we know that she’s specifically coming to see Chidori.
The second thoughts indicated by the Valentine’s chocolate is the primary clue at this point.
Most positive spin: she’s come to terms with her true sexuality and wants to make it up to Chidori.
Highly (not “most”—she could be a demonically-possessed serial killer) negative spin: she’s a player who can’t stand even a cutie she didn’t really want rejecting her, so she’s back for another go.
I loathe her so much I almost want to see the writing turn her into a sympathetic character somehow. Failing that, however . . .