As many others have said we have no right to control who other people are friends with.
However I would be pretty hurt that such a good friend would become friends with my “enemy”, not someone they were already friends with but developing a relationship with someone they knew hurt me.
Hell I don’t go to a local hairdresser becuase my BF has a beef with them.
I don’t think you should confront her though, you will end up looking like the crazy one.
I would just sit out a bit, build on other friendships, don’t do anything to directly cut ties with this one yet, see what happens, be careful what you share with her, don’t be the one to initiate contact, maybe be the one who is a bit busy right now, but don’t let anything blow up because you may really regret it later.