it sounds like the early signs of dementia. i would suggest dropping in on her more often and checking how many family members she remembers. she could also be getting a cold and that's all. keep a close eye on her for the next few wks to see what exactly it is. check that she remembers her address and phone number. take a walk down the street with her and observe if she recognizes her house when you return. get her an id bracelet with phone number of yourself or family member.