Putting down your daughter's friends indirectly criticizes her and shows your disapproval of her choices. Ask open-ended questions about your daughter's friend. If you've observed this girl engaging in behavior that you disapprove of, you can ask your daughter, "How do you feel when your friend teases other kids?" or "I've noticed that your friend never shares anything with other children. Does that bother you?"
Children can understand the negative behaviors and bad habits of others if you talk to them about how we all have parts of ourselves that we need to improve upon, rather than forbidding them to be friendly with anyone who is exhibiting some less than admirable character traits. If your daughter is too overpowered by another child's negative influences and persuasion, then you need to intervene and free her from that bullying domination.