If she hasn't done this before, has always been fastidious about her continence and has been in exciting situations and not had a problem, I would be looking at something going on medically.
The thing about medical incontinence is it isn't always consistent. I've noticed, even with myself, sometimes I can hold it all day, sometimes I have to pull over for emergencies several times in a day. She's a middle-aged gal like me and I'm very healthy for my age. Her bladder muscle may not be as strong as it once was and there may be something else going on, perhaps to do with her Fanconi, perhaps something else.
You are on top of the Fanconi…She's been consistently good until very recently....now she has accidents inside the house. I get the idea she's trying to get to the door, but not quite getting outside. I'm not convinced this is behavioral. I'd say give her the benefit of the doubt and have her checked for perhaps something else. (UTI, elevated blood sugar, thyroid, etc.)
Until then, try to keep her environment secure and calm. If it settles down, then maybe it is behavioral and you'll have to make adjustments to keep her on a level emotional platform. If she still has accidents, dig a little deeper medically.
Question: Does she act like she's ashamed or disappointed in herself? I've had one single incident with AJ...he had a case of the runs and went on a newspaper that I threw down, but immediately acted like he was sorry for it. (We were rolling down the road and there was nowhere to pull off.) If she behaves like this, then she doesn't mean it. If she acts like "So, there!" then it is probably behavioral.
I hope I've helped a little. Good luck with it.