i have seen my memory slipping too. it's worse in my dad. be sure to write down her favorite stories in a journal so they are not lost. i get my dad to dictate stories sometimes. i type them up and ask him to proofread. i am sure my descendants will be fascinated.

you can get a neuropsychologist to establish a baseline. if you test later you can see if the progression is slow and natural or rapid. you can also compare memory vs problem solving.