Assisting someone with autism

I've recently been given the chance to assist a girl with autism. I've done something along these lines a while back but the person I was assisting was high functioning and didn't need too much from me, just a gentle push and a reassuring smile and at most a walk to help calm down from a stressful environment. This girl Ill be assisting now is low functioning and has violent tendencys, wrether that be from her home life or from her disability im unsure. I actually knew her when we were kids and she, on multiple occasions, caused me extensive physical harm and made me feel unsafe. I understand a lot more about the struggles she was going through as a misunderstood and undiagnosed child now that I'm grown though and I'd like to help her in any way I can and to do this I thought Id ask if anyone who's done something similar or who has autism could give me any tips for interacting with her in a safe way that she feels comfortable doing (I have no way to ask her myself until we meet and Id like to prepare to the best of my abilities before hand)