My mom has MSA (multiple system atrophy, a bit like Parkinson's on steroids) and has recently been forced to give up playing the bagpipes because she isn't able to properly seal the holes on the chanter anymore. She would like to continue playing music so she has decided to go back to playing piano. She played for many years before taking up the bagpipes. I would like her to enjoy it for as long as possible so I'm hoping to find some arrangements of classical/"adult" music that don't require too much finger independence. I'm thinking a note or two per hand max but I'm open to suggestions. Slower rhythms might also be a plus. Any recommendations?
She could have some fun with layers of sound. That is, she can play duets/trios/etc. with herself, by recording herself and playing with her recording. I had a housemate who played flute duets with herself in this way. Your mother might need four or more layers to get all the notes. She can do trial and error to find out what works for her.
Another analogy: I used to accompany my children for their Suzuki pieces by picking out some of the notes from the piano accompaniment.
You may be able to pick up a lot of sheet music and piano books for a small amount of money at a used book sale. The big ones in college towns include sheet music and music books.
An alternate idea might be to get some play-along books+CD. Then she could, for example, play the bass line (normally the left hand), but use two hands. In this case she would not need to record herself.
She might want to branch out into jazz piano. It could be interesting and fun. I especially like the Bradley Sowash series of jazz pedagogy for piano.
Have her experiment and then report back!