My cat is 20 years old and having lost most of the spring in her legs, uses her claws to clamber onto furniture etc..

This morning I notice that she only extended the claws in one of her front feet which made it harder for her to climb, although is managed eventually.

She hates anyone touching her paws but I managed to check that the claws were still there and I could see no blood or obvious injury. She isn't limping and doesn't seem to be in any discomfort.
Any idea why she has suddenly stopped extending these claws?
Yve