Mom goes through a ginormous box of Depends paper underwear (80 per box) in about 8 days. So about 10 a day. Does this seem like a lot to others? It's very expensive at this rate of consumption. Plus, she seems to live on the toilet; that's where I find her most times I come to visit. I think she sleeps there. Not safe but no falls that I'm aware of from the toilet, yet.
You definitely don't want her to remain in a wet panty, so if ten a day is what it takes to keep her dry, then ten a day it is.
Is it possible for you to spend the entire day with her occasionally to see how it goes? Maybe she thinks she is supposed to change every time she goes to the toilet whether it needs it or not.
Just as an FYI, not a hard and fast guideline, we are at two a day, sometimes three. But I'm not sure you could say there is a typical number per day.
If she is changing that often perhaps an incontinence pad would be sufficient during the day? Some people also use a liner inside their pull up, but I have found that because there is a wet proof barrier on those large amounts of urine will not pass through to the pull up but leak around the legs instead.