you could always preempt the potential by being honest. That does NOT mean you have to reveal the details of what you think of the other person but simply that they are not someone you want to have around when hanging out. You could make it clear you're not judging them for hanging out with that person but that for your own reasons you'd rather it not be with that person hanging around too. Nothing wrong with that. A good friend will respect and understand your personal reasons without probing for details.

I dont' think that leaving out that specific information would be the best because that means everytime she wants to hang out you'll have to repeat the process of going around in circles avoiding mentioning the person you are trying to avoid. Just my take.