Ginny's hair is extra bouncy, outfit extra cute, eyes extra bright - well, if she had a tail, it would be extra bushy. She is feeling great about the spell last night - there were a few twinges of guilt when she heard there'd been damage, but it doesn't sound like anyone was hurt, so the guilt didn't really last.

Also, she knows she will see Alec, at least during history.

Thus the hair. And the outfit.