hi J.,
I feel for you and for your daughter, she is obviously going through a difficult time. You've gotten some great ideas from the other moms here. My oldest went through something similar around that age, your daughter might just not be a 'follower' - you could have a potential leader on your hands and that is not a bad thing. It's possible the kids in her class right now are not anyone she wants to be friends with and there could even be good reasons for her lashing out at them. I'm not doubting what the teacher observed but teachers have their hands full these days and there could most definitely be more going on than meets the eye.
I would talk with her, let her know how likeable she is and that everyone goes through periods of time when they're between making new friends. Then ask her who she would like to have as a new best friend and if she'd like to have these potential new friends over for a pizza party or similar activity or outing (movies - High School Musical, mall-walking etc). I would tell her about going through something similar at her age (or a friend that did) and then tell her how you (or your friend) worked through it.
Phone the parents of the kids and do the inviting to this party yourself to prevent any mis-understandings.
If she is not interested in getting new friends it could be that she was so deeply hurt when her friend moved away she doesn't want to risk that hurt again and she might need to work it out with some counseling. I wouldn't push her to do something she doesn't want to, or take things away - she is already hurting and she needs to open up to you, not go into a deeper sulk.
When my daughter went through what you're describing, she finally got involved with a church youth group and made some great friends and it pulled her out of her anti-social and sulking behavior. It was just a stroke of luck that she found that youth group - because she certainly would not have gone willingly had I suggested it - one of the kids she wanted to be friends with invited her along (after her pizza party I described above) and it really turned things around for her.
hugs,
W