Now in the rp I know I said I want slow regression but I think some babyish stuff should start now. Basically he should maybe teasing her a bit about how childish she is acting and comment about her accidents and not let her forget that she has a wetting/ messing problem untill she starts behaving and stop fighting him. She will try and push him away as always until she starts to relax and just accept babyish comforting. He should use embarrassment has a form of punishment. However we shouldn't go to full on babying just yet but definitely buying some training panties or at least an embarrassing plastic sheet for her bed and checking her panties and maybe taking her to the toilet like a child I love small things like that
but in the end it's up to you surprise me these are just suggestions