i am really sorry this has happened to you, and very sorry for your friend too :( What an awful situation for her.
However I think you sound like you handled it really well, and did nothing to provoke the assault, nor could you have done anything to stop it happening.
How you can change though is in the way you deal with it. By not reporting it (for whatever reason) you have just allowed yourself to be assaulted, you have made yourself a martyr and you have not asserted any form of authority.
If you are comparing yourself to your mum, and would wonder what she would do differently, I imagine the answer lies in whether or not she would report it.
Yes it would feel difficult with your friend, but if the roles were reversed would you expect her to keep quiet? And if she chose to go to the police you would (presumably) understand?
who knows, the prosecution might actually offer some help to this woman, who sounds very much like she needs it.
Good luck, I hope it all works out for you, and I am sorry if I sound harsh.