My mother wont go to work, iin?

My mother won't go to work. She says that she will go next week, but next week never comes. She only has to volunteer for few hours on a monday from nine am. I don't understand why, she used to go regardless. When I asked why she won't go, she said now isn't a good time, and that next week is better. I then ask why she doesn't just quit, but then she gets all defensive and says something the lines of 'no, i'm not doing that'. She does go whenever my dad drives her there (they're divorced, so not often). I tried getting her out of her rutt today by waking up extra early for her benefit to remind her to go to work. I told her she needs to go to her work, she said 'next week is better' (hence the same argument above, as usual).
It's not an issue of being tired either. I went to bed much later than her and I woke up before her for her sake!

What should I do? I feel useless, like I should give up on her reluctance/laziness issues. I try to help, by issuing my concern and using persuasion and reason, but it just leads to frustration. She doesn't want to admit her problem and just continues on doing her daily same routine of housework. It doesn't take that long anyway, and she usually finishes after making lunch. She then just watchs TV and falls asleep at her chair before being told to go to bed (again, not for my benefit, she is obviously tired - but that is another issue entirely)

Please help me