A.C.
You need to keep up her courage, encourage her, tell her she's doing well. Kids who have an Autism Spectrum Disorder (like my daughter, who has Sensory Processing Disorder) tend to be really hard on themselves. They don't think they're good at anything. Or that so-and-so is SO MUCH BETTER than they are. You have to continually tell her she's doing a good job, to do the best she is able to (and that that's all anyone can ask of her, that she gives it her best shot).
It is hard, I know. Just keep your eyes and ears open (maybe the girls are telling jokes and she doesn't get them? Maybe she makes a remark that is off or inappropriate or doesn't really answer/have anything to do with what the girls are talking about, so the other girls give her odd looks? All of those have happened to my daughter).
My daughter has been in dance since she was 4 years old; she will be 13 in April. She is thinking that this year might be her last year in dance. Not because she is big and large-boned and has a tummy (when all of the dancers are slender, slim, no fat on them)--although that does bother her (but she's started watching what she eats and she just started an exercise program--all on her own) but because she wants to become more active in school programs/activities (they introduced Lacrosse this year, but only for 8th graders. She hopes they will have it next year, because she wants to do it. So on her own, she has decided to get herself into shape so that she's ready to play! I am SO HAPPY and proud of her for taking the initiative on this!).
I can't "make" my daughter do anything; these kids with sensory issues/SPD issues can be quite stubborn when they decide to be! However, I encourage and support her when she makes the decision to do something. I would listen a little bit more and try to find out why, all of a sudden, your daughter doesn't seem to be interested in sports when she used to be. Is she a little chubby? Is her equilibrium off? Is she uncoordinated (and do the kids tease her about it)? Once you know the reason, you can help her formulate a plan to take care of her fear(s).
Good luck.