I brought my mother (89) to live with me. I can't get her interested in doing anything. Advice?

What kind of things did she do before she came to live with you?
When my mom was on her own I now realize she must have been terribly bored as she couldn't get out on her own and there really was nothing for her to fill her days other than radio and TV programs and phone chats with friends. I think to some extent they learn to deal with it or they would go stark raving crazy, but as a caregiver it is difficult to watch!
I agree with Blannie, include her in outside activities, even if it is just grocery shopping. Find a few chores she can help with around the house, dusting or sorting/folding laundry. Music always seems to be a favorite, as well as old time programs if you have access to them. And my mom liked listening to books on tape, I guess they are probably all digital now lol.

Is her depression treated, i.e. is she taking medication for it? What are you trying to get her to do? With my mom (who is 96), I found if I would say, "Do you want to do this or that" she'd say no, she was too tired. So I changed my strategy to say, "We're doing this or that." I'd get her dressed and we'd go. Sometimes she'd fuss and say she didn't want to go, but if she was OK, I'd push and once she got out, she always had a good time (and would say so afterwards). Would something like that work with your mom?

What are you trying to get her to do? Start small, just to get her in the habit of getting out and doing something. Then you can move to bigger things.