You can't control what other people say and do, only yourself. Worrying about what others say and think about us is more about how we feel about ourselves than about the other person. If you feel good about yourself, you don't need to worry about what others think. You moved on from the former friend who was not treating you in a way that was acceptable, which is sensible. I suggest you have respect for your other friend to make up her own mind and yes, support her if she has difficulties with this other person. Just because she is quiet, don't assume she is easily swayed, poisoned or will change her mind easily about you. Be a friend, trust and above all respect her. I wouldn't feel comfortable with someone who didn't think I could think for myself. In fact I would feel insulted.