Mom has fantastic genes so it is not unusual for her to be an active 91 yr old. She walks the neighborhood every morning. The past week she is finding herself tired most of the time. I noticed that her tiny appetite is even smaller. I told her this is normal. Is it?
Perhaps some nice cool summer soups might help as well, or fruit in juice, such as canned pineapple.
Potassium can be depleted easily if she's taking Lasix or other diuretic, or like me, eats a lot of celery. Anemia is insidious - it affects not only her physical energy but that in turns affects her motivation - at least that's been my experience. If you're feeling weak and/or tired, you don't feel motivated to do much except rest.
I think perhaps she should see a PCP or internist and get a full blood panel as a start.
From your description, she's always been active so this current condition isn't consistent with her history or lifestyle.
There also could be other factors....in what area do you live? Has it been unusually hot, such as in the high 90's or 100's? Does she live in an air conditioned house? Heat can have a devastating effect on anyone, but more so an elderly person.
See if she'll drink a big glass of water a few times a day, in addition to other fluids. It may make the difference of night and day.
If you have a blood pressure cuff, check her BP. If it's really low, that also can show she needs an adjustment in meds. 120/80 vs 100/60 MIGHT also indicate that, with her tired symptoms, she needs a meds adjustment. In which case, a call to her doc is warranted.
I'll also say that, at 91, she's due for a dramatic slow-down...
My parents use to walk 2 mile a day when they were 70's and 80's, but now they are in their 90's, Dad is lucky he can walk down to the mailbox using his walker. And Mom has slowed down a lot, too.
As for appetite, for someone who had been active, once they slow down, so does their appetite. As long as your Mom is eating a balanced meal daily, I wouldn't worry.
Do have one question, did your Mom have any changes in her medicines, such as now being put on blood pressure pills or said dose had been raised? That will zone a person out, big time.