My mother does not want to participate in our holiday celebrations anymore. She says she'll be fine. Is this normal?

My mom says she has never minded being alone (divorced 30 years ago, no others since). I have a sister and a brother, both of whom live very far away, but who she loves to hear from and looks forward to their rare visits with great joy. She seems very peaceful about her life in general. She goes out in her car each day to do simple errands. She spends her home time watching news programs and doing Soduku puzzles for hours on end. She has always seemed to enjoy the company of our family of three and my father in law. This holiday withdrawal appears to have started over a year ago, concurrent with an onset of mild-moderate mental confusion and forgetfulness that seems to be increasing. She will not share what she has discussed with her doctor. She will also not fully explain (or can't explain) why she doesn't want to celebrate the holidays with us any longer. She has said that it confuses her to sleep away from home. She says that I am so busy with all of the preparations that she can't spend time with me anyway. We live an hour away in a very traffic congested region, so it would be very difficult for us to pick her up and bring her back home on the same day, when that day is a holiday. I have offered to do this, though, and she has refused. She won't stay overnight, because she becomes more disoriented at night, even if I sleep with her. I am in the middle of trying to please my family and include my mom in the holidays some how. My best friend said to take her at her word and just carry on without her. It is heart wrenching for me to think of her all alone on Christmas Day, though we did it last year and everyone survived. It just seemed so wrong. I don't want to separate from my own family. Any suggestions? Thanks so much.