I don't feel sorry for this girl
Really ?!? Why don't you feel sorry for her?
Because she hurt my feelings for no apparent reason.
It is okay to feel hurt that somebody hurt you but it is not good not to feel empathy for them. You don't want to become like them.
She started it and I'm going to keep it up.
I know the urge to retaliate is strong, but its much better to walk away from the situation. Don't engage with her negativity, it will only bring you down to her level. Just keep being positive and try to surround yourself with other positive people.