Oh, Goodness, thank Heavens it wasn't a chld she hit that crossed the road without looking!
I'd be inclined to go up to the woman who hit the other car and tell her, loud enough for everyone to hear "I just wanted to say I hope there's no hard feelings with me having to give a witness statement about your accident, I understand that with you being over the limit you could lose your licence which could be terrible with you having to ferry children around, but tbh, i really have no choice, I feel awful about getting involved, but I spoke to the officers at the scene and don't really se how I could not give evidence, I would assume if you weren't too high over the limit you'll be ok, Good Luck"