My mother-in-law pees all the time in the bed and in her rocking chair. I don't know what else to do. Advice?

According to your profile, your mother-in-law has Alzheimers. She can't help it. You need to purchase a type of clothing for Alzheimer's patients that closes in the back, so she can't get to her underwear. If you google "Alzheimer's anti-strip clothing" you'll find some options for one-piece jumpsuits that close in the back. Good luck!

Can you find an old style body suit with snaps at the crotch, put on a depend and fasten it up?

Throw away all of her panties and just put depends in her drawer.