I would tell her, he sounds like a complete SoB. Sometimes they dont blieve you anyway, I told the girl thats with my ex to be careful cause he likes to hit, and shes like omg he would never do that to me > 6months later ... "I should have listened to you", now shes stuck with a newborn baby an he is in jail.
Dunno why, but I think you should tell her or get someone else too lol.