From what you've posted, I know that your husband isn't always open to your suggestions, but perhaps he could be convinced that it would be in his mother's best interests to humor her in a way that didn't exhaust you and waste her money. And you could help preserve her dignity, even if she doesn't realize it needs to be preserved.

The last couple of years my mom was alive (with Alzheimer's), I realized that humoring her sometimes meant (gasp) lying to her. There was no point arguing with her reality, because it WAS real. If she said "Nobody has checked on me in 12 hours," I gave up trying to explain that it had actually been 45 minutes since I'd gotten out of bed the last time to check on her.

She just didn't believe me, and was upset because I was "lying" to her! So the next time, I just apologized and said, "We'll try harder to get in here more often." It was all she needed, and she would smile and pat my hand and say, "That's all right, I know you do your best." Sometimes I'd go back to bed and cry, but it was still better.

I know your MIL isn't my mom, and the situations are different. But can she really tell the difference between a diamond and a zirconia? Sometimes giving a demented person what he/she wants isn't the kindest thing to do after all.

Perhaps your husband might be persuaded that encouraging his mother to dress all Victoria's Secret-like and put herself in the position of losing even more dignity might not be the kindest way to humor her. I know, it isn't that simple. I've been there, and about a million times I've thought, "Easy for you to say" when people gave me advice. But we do care!