ACF shedding excessively

[Toefrog]

Hello all,
I have a group of African clawed frogs living in a 40 gallon tank. They have lived there for many years with no problems. Recently my oldest (roughly 12-13 yrs old) has begun to shed constantly, and it’s coming off in shreds instead of the normal clean shed. She’s also spending more time at the surface than usual.
I read that this could be due to irritants in the water but all the parameters are normal when I check. I’ve been doing every-other-day water changes even so. All the other frogs are healthy and seem unaffected.
I’m looking for advice as to what this could be and what I can do to treat it. Are there any medications that could be helpful? Could it be a sign that she’s growing old and declining? Thanks for any advice.