Lois, that is just plain weird. But like Gabriel says, if its dementia, nothing is going to change it.
I wonder if you made it into a big joke and arrive wiht a pillow strapped to your back end, if she'd take the hint. If not, than at least you have a pillow there when she attacks.
I feel for you, I bet you are sore. That's just plain weird she does that.
Or, you know those paddle balls that have a wooden paddle and the ball is attached with an elastic string? get two of those, remove ball and string and put one over each cheek inside your pants, then if she hits you, she hits wood. Maybe it will get the message.
This is totally irrelavant, but..... When my dad was a kid, he had some "strike anywhere" matches in his back pocket. He got in trouble for something and his dad was spanking him. He started really yelling and my grandfather said, he was really going to give him something more to yell about and apparantly hit him harder (this was the 1930's, so discipline was different then I guess).
Well what was making my dad yell was the matches ignited. When smoke started drifting off my dad's behind, my grandfather apparantly stopped in amazement. He never spanked my dad again after that. That has always been a huge family story and supposed to have made me feel better when I was litttle and got a spanking. I guess I was to be thankful my butt only "seemed" like it was on fire.