I've been thinking about writing a story where a mother's continence is inversely linked (psychically, magically, whatever) to her young daughter's potty training. Wouldn't be physical regression or mental regression but I guess, just potty training regression. Basically when the daughter starts potty training, the mother starts having little accidents here and there. As the daughter gets better at using the potty her mother gets worse and worse until she's completely incontinent and humiliated that her own daughter can make it to the potty but she can't. Maybe there would be mental regression at the end but mostly would have the mother being perfectly capable otherwise.