My parents have always said if there is a bathroom, I have to visit it.

MK seems to have the most bathrooms. A bathroom is never far way in MK. The only problem I have with the MK bathroom setup is that there are no bathrooms near the bus stops. The only bathroom is near the ticket office and with the security barricades it is a longer walk to/from the bathroom and bus stop.
EPCOT is so so and the bathrooms seem to be more hidden. In WS they seem to be very spaced out especially when one has been sampling beers at F&W.

But at least there is a bathroom near the bus stops.
AK is ok I suppose but the bathrooms are well spread out and there is no bathroom when you get off the train so you have to skip the animal trails to find the bathroom. It seems like there is more distance between bathrooms in AK but they are there. Eventually. No bus stop bathrooms. Why, can't they have bathrooms at the bus stops?
DHS is a bathroom nightmare. I THINK I know where they all are but for some reason they just seem hidden to me. Maybe because DHS is not my favorite park. Heck, maybe this is why DHS is not my favorite park.

The bathrooms are kinda far away but not too bad for the AKL/AKV bus stops.
No problems at TL and BB in finding a bathroom.




Kidding.
Thankfully, I don't have bladder issues but I do drink quite a bit of water and when it is time to go, it is time to go so I understand the OP's concern. Before getting on rides I ask the family about a bathroom stop even with a FP. You just never know if there will be a breakdown on the ride. We avoid the monorail now because it seems to always have a problem. One of my nightmares is having to go to the bathroom and to be stuck on the monorail...
Prince Charles once said something to the effect that one should visit the bathroom as often as one could because you never knew when you would get your next chance. Makes sense I guess since he can sit for hours at some ceremony. I think of Prince Charley when I see a bathroom and wonder if I should visit.
I would make sure I knew where all of bathrooms were located at the park we were visiting. Maybe give Mom a park map so SHE knows. Hopefully that will make it easier on her.
Later,
Dan