@monkeyblonde
YANBU to feel hurt/offended/slighted. Don't feel bad about it.
As has been said though; go to school tomorrow and smile pleasantly, say hi, and walk on.... Don't mention to ANYone that she has unfriended you. And pretend you haven't noticed.
For the younger generation a FB 'unfriend' is a HUGE snub, and I don't think some people realise it.
Please don't feel too blue; she has probably done the same to a few others. Probably having a 'cull' of people who are simply acquaintances. Nothing personal.
One of my friends got really upset recently, over someone she thought was a friend (a neighbour of hers, 10 minutes walk,) who didn't send her a Christmas card, (even though she sent her one.)
She has stewed on it since about the 23rd of December, and is baffled and hurt that the neighbour never sent a card. No idea why the lass hasn't sent her one as she always has before. She has still been smiling/waving when passing my friend, but my friend still has a bee in her bonnet about not receiving a Christmas card from this woman!
It seems trivial to some, but like the FB unfriending (with the OP,) it's NOT trivial if it upsets someone.
I would not call the woman in the OP a bully of course, but YANBU to be miffed.