HELP!!!

My 14 y.o keeps vocally stimming. It's driving us crazy...

Some days she'll just flap her hands and rock. But, the other days she will become really loud making so many noises with her mouth: really loud hums, squeals, she will even bite us without meaning to, she will bite her hands (she came home with many bite marks on her hand from school), she will quickly close her jaw together to make a snapping noise. She also runs and belly flop on the couch and beds. She never did this when she was younger... But what really worries me is that she will put anything in her mouth. When the stimming happens, she becomes very emotional and angry for no reason.

We have got some chew toys for her but she won't use them and when she does, she will chew it so much it will break apart and she will start eating it without us even realizing. But what really confuses me is that she is extremely intelligent and knows that she can't put things in her mouth and doesn't usually. (This only happens rarely and only started doing it last year. Whatever she puts in her mouth ie. play dough, she will spit it back out ). (When she was younger she had put a coin in her mouth and swallowed it but that was the only time she put something unedible in her mouth) so I'm really confused why she's doing it a lot now...

Does anyone have any tips on how to reduce the stimming and how to stop her from biting herself in school? 

Any advice is appreciated! 

Thanks x