Bullying rarely goes on in the classroom, and a lot of bullying, even boys, does not involve physical assault.
My high school teacher DD would disagree -- and she would really disagree from her time as a MS teacher. It's astounding to me hearing from her experiences and those of her teacher friends from college who are in a wide variety of school settings just how much bullying and fights are commonplace today, even in comparison to when my DDs were going through school.
OP, this is a really tough thing to be going through and I hope there is a good resolution for your DD very soon. A few things in your situation stood out to me based on my experience raising two daughters and anecdotal experience my teacher DD shares about what's going on in schools and classrooms today. She teaches special ed and most of her caseload actually stems from students with emotional impairments and/or less profound cognitive impairments. A lot of what stood out to me in your comments tweaked things my DD has talked about struggling with making parents of various students understand/believe regarding their children's real struggles.
I am going to challenge a lot of the prevailing attitude in the thread and caution you to ask yourself, can you really look yourself in the mirror and say with absolute certainty that your DD's therapist is definitely wrong in suggesting your DD is being manipulative and should remain in the classroom? That's a pretty strong position for a therapist to advocate. You describe your DD as sensitive. Is she perhaps being treated for anxiety and avoiding school because of anxiety more so than actual bullying?
Bullying happens. It can have devastating effects. It shouldn't be overlooked. I'm merely saying that the bottom line is your daughter needs a solution for the real problem. If bullying is your daughter's true problem, that's where you should focus your energy. If it's not truly the root cause put your energy where it's needed to solve the problem.
If the therapist isn't working towards what your DD needs, find a new one. If the therapist is working on the issues and your DD is resisting, don't encourage the avoidance. In the end that won't help your DD.
It's great that she's participated in some activities and enjoys some things. Unfortunately theater can be a very tricky dynamic in and of itself. Competitiveness can make interpersonal dynamics difficult, and even adult theater groups struggle with that issue. Breaking into established cliques can be difficult because of the potential threat to pecking order a newcomer brings. Helping out with childcare is a commendable endeavor and enjoying dance is great. Unfortunately both of those do nothing to solve her social issues at school. A way to make inroads into the school social scene may be participating in task-oriented groups and activities where there's a common goal and simply a shared workload or project. It can be easier to make inroads with others if they get to know Sarah as the cheerful girl who worked hard with them to get all the tables and chairs set up quickly instead of another rival for the lead role in the musical. Participating in the things she loves is great, she just might need to participate in some others as well to give her the opportunity for the ice to break.
Maybe she needs not to attend that school. Maybe she needs a better therapist. From my perspective I certainly can't tell which choices are best for her. I am encouraging you to be very objectively honest with yourself about everything you know so that you can shortcut a path to working towards a solution.
Very best of luck to your DD and you.