Is increased sleeping part of the last stages of dementia?

My 89-year-old mom has had dementia for the past 13+ years. She currently resides in a ALMC facility. She has had 2 ER visits since the first of the year, one from a fall due to a UTI, and the other resulting in a 3-day hospital stay due to aspiration pneumonia. She was previously sleeping until around lunchtime every day, but recently, has begun sleeping until anywhere from 2:00 till 4:00 every afternoon. Occasionally she will get up early but is mostly sleeping 15-17 hours a day. Is this part of the last stages of dementia? The nurses are telling me she has lived a good, long life and to let her sleep if that’s what she wants to do.