I think if it was my dog, I would just try to adjust her diet so she has great stools. Here is an article about bowel management in incontinent pets. If your dog is doodling in the house, it is a minor issue when the stools are firm, low odor, and not sticky.
viewtopic.php?f=5&t=18586
The problem with diapers is, she's a girl. Waste that collects in the seat of her pants will be contaminating the private area where the urinary tract is, and you risk an infection.
Did you already take her to the vet to have it checked? If she has had a change of bowel habits, it seems like something is different in her digestion and you may have to be Sherlock Holmes to figure it out. Perhaps some acidophilus would help. For example maybe she was given antibiotics for something and they affected the good bacteria in her gut. My dog got something called bacterial overgrowth which made her potty a lot, and it was messy. I think she was prescribed flagyl (going from memory right now) and it cleared up.
The vet may have other ideas of what to check, but a senior wellness exam might be a start.
Another idea might be to check whether they changed the formulation of her food. Perhaps a new ingredient is making her gassy or something.
Do you have a new pet, where she is perhaps snacking out of the kitty litter box, or cleaning up after another dog's duty in the yard?
Not sure what is causing it, but I would just try to address stool quality while you figure out what is going on.