Am i over reacting?

There is a girl in my class whom i once considered to be a sort of friend. My friend group considered her as a true friend, but I had an off feeling about her. When i first met her, (i am quite a socially awkward person) I complimented her as she is quite pretty. It must have been a weird compliment to her or something, I know it was a weird compliment (i dont think it wasnt anything insulting so don't worry,) as I hadn't said anything to her at that point in time, so I guess it was a shock as she reacted very dismissive and annoyed? I'm not too sure. That was a few years ago, and in that time she did a few things, for example, insulting people (saying that their short hair made them look like a child, but she loved that for them), telling people they could only be friends with her, physically dragging people away from boys she liked, insulting people about things they were bad at (saying that they were bad at a sport in front of older boys, when she was no better) etc.

I thought that i was just being over-dramatic about it and was making things seem worse than they were as she was very cold to me, and to be honest so was I, although part of that was because we had nothing in common.

Recently, people have told me that she was insulting them as well, e.g. Girlfriend is quite short and has a tall boyfriend and this girl insisted on putting a sticker (?) of his back. Girlfriend came and took it off and this girl then said "put it on his forehead, she can't reach it."
Not only did she insult the girlfriend to her face about her height (and girl is quite tall), but also insulted the boyfriend about his height and forehead(something he is teased about often)
This girl also insults people in the musical that i did recently, which is weird because her sibling is in it, and they said they enjoyed it.
There are many other situations that i can't fit into this post. I wanted another opinion on this as it can't be a coincidence. If you want more info i can say in the comments

I have managed to get my friends to withdraw from her as her comments were starting to affect them (test scores, looks/appearance, preferences etc), but not by completely cutting her off as I was worried we could get into trouble for that as we have before. Was i right for this or was i overreacting?