Mom is 86 with dementia. Doesn't read or knit, just does nothing. Doesn't even want to put her teeth in. Any suggestions?

Apparently she has been seen by a doctor, since you mention depression medication. Since her work was here life, she likely misses the social aspects of work. Have your thought about adult day care or even assisted living?

You could begin with adult day care and see if the increased socialization perks her up. If, after an adjustment time, that does the trick, adc may be your answer.

Otherwise, it seems like she may benefit from having others around in an assisted living environment. The way she is, she's likely to just waste away (which you realize or you wouldn't have asked). I hope you can find a social outlet for her. Expect her to resist at first, since that's a normal reaction to anything new. But you could very likely find that before long she could hardly wait for her time at adc. If she wants to "work," they'll let her work and help her feel useful. She likely misses that.
Good luck,
Carol