Hi speedy11
Is your best friend aware of the issues between you and her other friend? If not, then I would think there is nothing to be worried about. If she is aware, then I see nothing wrong with letting her know that you are a bit uncomfortable with their relationship.
I have a few friends who are friends with people I care not to associate with for whatever reason. Until my friend gives me a specific reason to worry, then it doesn't bother me at all. But that's me. My friends know how I feel about these other folks and don't talk to me about them and that works for me

sabby