Does your mom live close by or is she far away? Does your daughter know that she is the favorite & that Garandma feels "sorry" for her? This just might be a small part of the problem.
It sure does not sound like there is many dull moments around your house.
I had 2 older brothers when I was younger and they loved to torture me! Their favorite thing to do was to hide a potato until it was all mushy and had a bazillion arms and legs growing......(can ya smell it
) and one would hold me down and the other would wave it right over my face....sometimes they would mash in my face....& other times they would just hold it really close. Or they would sit on my chest and would put my arms under them and would have a string of spit from their mouth and would suck it up and sling it down RIGHT to my nose! It was sooooo nasty! My mom worked full time and my dad was never home, so they got to do what they wanted when they wanted. & I knew better than to tell on them. I was going to be alone with them again in a few short hours. I did get my oldest brother a few years ago though. He lives in Hawaii and my husband & I went to visit. I did one of their favorite things tio him that they used to do to me. In the middle of the night, I went in the bathroom and a greased to the toilet seat BIG TIME. Then I had to tell my husband not to use that bathroom. He thought I was being so childish! He never had to put up with this when he was a kid. WELL......eventually I heard my brother cracking up and cussing at the same time. I almost peed my pants and hubby finally found the humor in it. At least I was smart enough to do that to him RIGHT before we had to get on the plane!
Anyway......I am not sure why your daughter is doing these things, I wish you luck in finding the answer. I still think that you should try the Dr. Phil method and take everything away from her. Everything BUT HER BED! I know what a pain that would be, but it might do her some good. I am sorry that I can't remeber what all you have tried, but it sounds like whatever you do is going to have to be drastic!
Good luck & keep us posted!