To my shame I have shouted, a lot, at my dd. We were in desperate need of help and support, we regularly endured kicks, punches, split lips, scratches from her just trying to get her dressed and out of the house. Previously, I'd always considered myself a good parent as I never so much as raised my voice when ds was her age. I was never driven that far. Turns out dd is neurodovergent and highly anxious. I never shouted at her thinking that it was an effective behaviour management strategy, it was borne out of exasperation and anger when I was at my lowest (in my life). I am deeply ashamed of it, and there isn't a day that goes by when I don't regret it. There is no help for families like ours, with undiagnosed neurodivergence. I suspect that there are thousands of families who have been in our position (try seatbelt refusal when you have to get to work for getting your blood boiling) and are just too ashamed to admit it.
We educated ourselves (there is no 999 for mental health) and began to understand that she was not naughty, she desperately needed our help, and we were failing her. Over the past few years I have become much more adept at managing her extremes kindly, calmly, from a position of understanding and love. We managed to get some mental health one to one support following a period of complete school refusal (or avoidance, which is now common parlance) and slowly, slowly we have turned things around. There are days when I still have to count to ten, or remove myself from the situation, but I would die for our little girl in a heartbeat and I am now a much better parent to her.
I'm not saying this is the case with your friend, op. My reactions, whatever prompted them, at my lowest points, were deeply damaging. You might actually be doing her a favour if you do report it. If it's bad parenting, then she might be corrected. If there's more going on, then you'll have given that little girl a chance in life.
I'm sitting here in tears writing this, at the thought of what could have happened.