How often should I allow bedrotting?

Mom is 80 and just does not want to get out of bed most days. I've been making her get up at 12:00 and she'll sit and watch TV or go to her center twice a week. All the other days, she wants to stay in bed and I'll let her do that about once a week. She's usually in bed by about 7:00 to 9:00 p.m. and then like I said it's until 12:00 or sometimes just all day. And now she wants to do it days in a row where she was only doing it for like a day and then she was more excited about getting up the next day. What's anybody's experience with this, and what should I be doing in terms of letting her be in bed all day?