Hi, E., I'm sorry to hear how much you've had to go through. The regression your daughter is experiencing is understandable, though certainly inconvenient.
My Grandboy 3.5 is potty trained but reluctant to stop playing to go pee, so we've created quite a game out of it. He likes dinosaurs, so when I notice him doing "the dance," I will observe that there is a line of dinosaurs waiting to use the bathroom. I might even pantomime asking them if G can please use the potty first, nudge them out of the way, etc.
It's been fun for both of us coming up with variations on the game. Sometimes we race the dinosaurs to get there first, sometimes he shares space on the seat for one or more baby dinosaurs who just can't wait to pee, etc. Seems you could do similar games with fairy princesses or dragons or butterflies or whatever your daughter likes.
At any rate, it is often possible to make necessary tasks fun. Takes a little creative energy, but it turns out to be fun for the adults, too. For me, this in one of the great secrets of life – there isn't one list of appealing activities and another list of unappealing activities. ALL of it can be interesting, engaging, and even fun if we come at it creatively.
Good luck. I wish you good health, and an easier future for your family.