Hi there, went through something similar with my ds when he was about 2.5 years old. I started to use a shower head to rinse. Would let him play with it, getting him to help rinse, help rinse off soap on his body. It really helped. However, we did have to 1 time just do it even though he was kicking off, then in the middle of it he realised actually this isn't too bad and was fine after that. I was in the bath with him too.
Perhaps get in the bath with her and get her to wash your hair?