Does my Mother have Dementia or MCI?

My has trouble with her memory and with remembering names, solve puzzles or spell words. She is starting to get tired alot and the last few days falls asleep about 5 hours after waking up. Shane also wants to remain independent and he does not want help when offered, gets moody slot and thinks your telling her want to do so she gets mean and says mean stuff to you when I all want to do is help her. She makes me feels like I am stupid questions all the time. We played Dominoes last weekend and she was when I suggested it, however, we tried to play cards and couldn't remember how to.

She had a cold for a long time, then we discovered she was allergic to peanuts which kept making her sneeze. I suggested going to her doctor for a blood test but she refused as she doesn't want to appear to be a nuisance.

I am really worried about her. My sister's thinks she's ok as she still has a sense of humour and she still able to chores such as housework, banking and pay bills. What do you think?