I feel for you, KatyMom. However --
Your children ALWAYS come first. If your mom can't help herself despite your warnings, you MUST follow through. I'm sure one of her "loving sisters in the Truth" will be glad to take her in. (Watch how fast they will run away when they hear that!) But that's not your problem.
When my son was small, I had a similar problem with my dub mom (but not nearly as severe) . She had her own home, thank goodness, but whenever my son went for a weekend visit there, she would give my son dub books to read and talk to him about the truth, despite my repeated warnings not to.
I explicity told her that her continued relationship with her grandson was dependent on her not trying to turn him into a dub. Thankfully, I was able to counter any questions my son had about dubs. My mother knew I meant business about dub indoctrination and had the sense to only go so far and no further. If she had started in about demons, that would have been a deal-breaker.
The funny thing is -- my son (now in his thirties) still has those books my mom gave him. He never read them, but keeps them because he likes the colorful covers. He says they look nice on his bookshelf!
WTS propaganda as tasteful interior decorating. I still think lining the bottom of a bird cage is the best use for them, but to each his own.
Good luck with your dilemma.