I work with the elderly. Write 5 simple things down on a piece of paper and show it to your mother for about a minute. Something like: coffee cup, macaroni, high heel shoes...simple random things and ask her what she remembered about the list on the paper 10 min later. If she gets less than three she needs to make a doctors appointment to be tested for Alzheimers. Seriously. Tell her you are concerned for her and ask her to play along. Remember, let her look at it a full minute and ten minutes later ask her what was on the list.
Most of us do these things, stress causes memory loss as can early menopause, tons of stuff, but for most of us this is quite normal.
I recommend she takes ginkgo bilobas, twice a day. I take two 60 mg, one in the morning & one in the evening. Been taking them for 25 years along with my other vitamins. Have no memory issues at all.