I'm not sure where you are located (US?) but one option that could be explored is to have your school district foot the bill for your daughter to be schooled at home. At least until a behavior goal can be implimented on the I.E.P. and met.
From your description - it sounds as though she was doing well and then suddenly took a turn for the worse. That tells me that SOMETHING wasn't working. I am shocked but not surprised that your school gave up on your daughter. I would guess that your school district does not have behavioral specialist on site and don't have a clue as to what to do.
Are you working privately with a professional ?? Are there professionals in your area that specialize with kids ? If the school district is clueless .. then get to a specialist who can direct the school on your daughter's behalf.
The principal might be 100 percent dedicated, however, she is totally ineffective. And clearly has thrown up her hands. True dedication would lead her to secure the necessary professionals in order to provide a free and appropriate education for your daughter.
I wish you the best