A: The 7th grade is a classic time for many changes in friendships and social relationships, even long-standing ones such as your daughter has experienced. It is not clear to me whether you are concerned about actual bullying--in which case you might meet with your daughter's teacher to learn more about whether this "teasing" is a problem or simply ordinary 7th grade ribbing.
You can best help your daughter by being a good listener and respectful supporter. Explaining that many 7th graders share her loneliness and suggesting tactfully that she might reach out actively to get to know some fresh faces may help. Joining an activity such as photography or sports or a special club may be an avenue for forging new relationships. Follow the lead of her personality and interests, so that the brainstorming comes from her participation too. Paradoxically, your being a temporary best friend and spending time with her picking updated clothes, hairdo, and other mother-daughter teenage activities can boost her spirits to find new connections with her peers.