I think you have been given some very good advice by the other posters.
A girl in my youngest DS's class at primary school went through a period which her Mum described as a period of depression. Her Mum confided in her tutor who suggested she take a little time off. She actually took her out of school for a few days and let her decide exactly what she wanted to do. She decided to go to the zoo and to The National History Museum. She made it clear to her daughter she didn't mind which senior school she went to and assured her that her happiness was the most important consideration. Her daughter decided she wanted to go to the local grammar. Her Mum involved her in all decisions regarding preparation (when and how much). I think her intention was that her daughter would feel more in control.
Of course your priority is your DS's happiness and well being. It may be that you need to keep telling her this at the moment. I wish you both well and hope your daughter feels happier in herself soon. Do bear in mind that some girls seem to have a bit of a surge in hormones at this young age and this could be affecting her mood too. Lots of big hugs are in order I think, but I have no doubt you are already doing this.
(My post crossed with Herman's - those hormones are still plaguing me at 47!)