I'd plan a vet check up for her as this sort of thing could be incontinence, a result of intestinal parasites, or another health issue such as a nerve problem in the spine or hip pain leading to unplanned defecation.
She is getting to be a senior girl so this could be due to arthritis, a spine issue etc.
If you find there are no health issues you might consider if the problem could be related to the food being fed. Keep track of when she eats and when she has a stool.
It may be adding a spoon of canned pumpkin to her food will help her as that has lots of fiber making stool pass more easily. If she is on a high fiber food already maybe she needs to go to one with a lower residue.
Hope this helps you!
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics