what happens prior to the tantrums , what triggers them there is usually something, how does she get on at school is she happy there have friends,Get her involved in a club with some physical activities its ammazing how children love to work out ,do Gym, swimm, sports...when shes at home play board games with her , have fun ...
Have you taken her to get check out by the doctor? She sounds like she could have depression. I would call her regular doctor and see if he could recommend a specialist for you.