Any tips on how to ease skin soreness from sitting all day?

Patient is 92, female, wears Depends. On a walker from 2 broken hips and although we exercise and walk as much as she will permit she still sits many hours per day. There is no break down or pressure wounds but she complains of "soreness" on her bottom. It is not red but I understand what she is saying since I worked behind a desk 12 hrs a day and sitting on folds in my clothing all day made me sore as well. I know her skin is delicate and the fabric rubs her.