I'm sorry your daughter is having such a difficult time.
It is hard to give advice without knowing more specifics about your DDs situation. Are these perceived friends ones you/your DD has known a long time? Is the lack of reciprocation new? Did she previously enjoy more fulfilling relationships with them, or is this sort of how things have been going? Do you know any of the parents well enough to initiate a conversation about what you have observed? Does your DD seem bothered or upset by what you observe?
If you can't gain insight from talks with your daughter, can you spend some time in an atmosphere where you can better observe her interactions (clubs, parties, extracurricular activities, etc)?
It sounds like something I might want to bring up with the school counselor, depending on specifics of the situation. If the counselor is a good one, she may have insight into the cliques and groups that are forming around this age, and even how your daughter fits into the scene. However, she may not have that insight, and if your daughter is reluctant to talk it may be hard to gain that insight. Still, this would be a good place to start.
We have not experienced what you describe, but we have had a difficulty friend situation in the early middle school years, and yes, we found ourselves as parents declining invitations from a particular girl. In our case, the girl in question was engaging in relational/social bullying, and we tried but failed to resolve things first by talking with her parents and the school. At any rate, this does not sound like what you describe with your daughter.
ETA: you might want to read more about relational bullying- early middle school is a time of huge change for kids, girls in particular, regarding their friends and social groups. Depending on what type of school environment you have, I would look out for things like social climbing. This age is when girls can become hyper-aware of image and others' opinions, and many girls become quite obsessed with fitting into a particular mold or group. One of the ways they facilitate this is to sacrifice, or put down girls who may have been friends previously but who are not aware enough or interested enough to play that social climbing game. It gives the climbers currency with the "in" group they aspire to join, and can be incomprehensible (and damaging) to those left behind. If this is what's happening, a good counselor can be of help.
