Could it be an issue with puberty?

Is she in any kind of therapy? My daughter has Asperger's, not autism, so it's different, but she used to bang her head on the wall, dig her nails into her arms, try to rip hair out of her head, scratch up her face, not to mention all the things she tried to do to me. I got her into play therapy and that helped. She no longer resorts to self-mutulation and does not lash out at me nearly as much.
I also asked her pediatrician a safe way to hold her to keep her from harming herself- with me on the floor and her in my lap, holding her arms crossed and rocking back and forth seems to calm her down.
For the times that she needs her space, instead of time-out, which never worked for her, she now does art therapy where she paints out what she is feeling. All kids are different of course, but mine has great difficulty expressing feelings clearly, so art, dance, etc. are very helpful for her- and myself as well.

I took my son to Emergency Room and they referred to intensive outpatient treatment...this was like 5 days a week during school hours...3 hours therapy and 3 hours school work done online...when he was in trouble at home...he was in trouble at the facility...and when he's in trouble at the facility - he was in trouble at home...there was family therapy once a week - this is what helped us...while he was there...he absolutely hated it...read my story for more details...

Medication? I know some ppl are opposed, but we've had great success with Abilify. Occupational Therapy was also helpful in helping our daughter gain coping skills & strategies so that she'd be able to recognize the signs her body gave her before she exploded and deal with the feelings before they escalated to that point.

My daughter had tantrums so bad that it took 4-5 adults to hold her (therapeutically). I adopted her at 9 yrs old. One could barely understand what she was trying to say at times, she had more food on her shirt than in her stomach, and the tantrums were the worst, she was always sorry afterwards, but her brain was not functioning well, that was apparent.
I started her on B vits, with extra B12, sometimes i injected it, but that got old. D3 improved her mental status quite a bit. For the tantrums, the doctor put her on wellbutrin, and I added Valerian, and Melatonin, although used for sleep, they can aid in calming and preventing outbursts, which cause damage to self-esteem, relationships, and school in general. I still use these supplements for sleep! there is alot out there, try one thing at a time, but with a few months it made all the difference. There is a book written by a woman psychiatrist with an Autistic GD, and although its overwelming at first, its a great resource. I can't find the book or remember her name, but when I do I will post it. Remember the organ first to react to low oxygen or blood sugar is the BRAIN, what is it doing without nutrients? Out kids have great needs than the rest of people who can get by with a good diet. Hope this helps, I also used Hippotherapy. Peace to you, Susanne