The parent teacher conference sounds like a great start. If that doesn't seem to shed light on it then perhaps a visit with a counselor, psychologist etc who may have experience with girls in puberty, get some sense of how seriously to take her comments, etc.
Polly
So much of what happens with girls is under the radar, but the teacher may be able to give you another view of what's going on.
I think it is always a gift to give kids a chance to see someone "professional" to help with their problems. If you find the right person, it can help with the current issue. And it helps our children see that it is ok to ask for help. It's a good life lesson.
If your child is involved with activities outside of school (teams, casts, clubs) see if you can help her cultivate friendships in those circles. I have found that if you are "out" with your group at school, it is helpful to have another group to pal around with.
Hang in there. This is hard.