Are you under a Paedatrician at all?
If so, I would be seeking some clinical psychology input to support with difficult behaviours, and possibly a conversation about safety planning. (If budget stretches, I'd see someone well-regarded by families locally, privately, just because the demands of secondary transition, plus puberty, are enormous, and any support you can wrap around both you and her at this stage would be helpful).
Does she have an EHCP? Is there any SEMH provision for her included?
She's very lucky you get it, and understand the origins lie in her anxiety - being compassionate and not blaming her is so important to her self-esteem and your relationship. Is there anything more you can do to work out specific triggers, and adjust the environment accordingly? If things need to give, and demands on her need to be reduced, can you roll with this, in order to keep her in a zone of regulation more of the time? I know it's difficult, if a lot of this is to do with the stress of a school environment, which ends up being played out where she feels safe at home.
Do you have some support of your own where you can vent? Counselling/therapy can sometimes be a lifeline for parents coping with violent and challenging behaviour.
Some people will suggest seeking a social care assessment. I'd suggest proceeding mindfully here; if you are contemplating this path, try and get assessment by the disabled children's team who will understand this situation. Unfortunately funding cuts mean autistic children are sometimes (potentially unlawfully) excluded from specialist services and assessed by generalists who will work from a perspective informed by safeguarding and an interest in identifying parental deficits. Whilst this can still be helpful, it can also be a mixed bag, and some people have unnecesarily difficult experiences due to poor levels of understanding of the challenges autism can pose within families, and a lack of familiarity with appropriate strategies.
Sending you best wishes. Although it is a bit of a taboo topic, lots of parents of autistic childrenn experience this. Because of the developmental lag, in practice you are parenting a much younger child. The situation will improve with age as her cognitive abilities, including self-monitoring and self-regulation, develop a bit more and better strategies for expressing distress and discomfort become available to her. Try and prioritise your relationship and everyone's well-being, even if other expectations have to give in the meantime. 