Omak = ooo I like the redirecting energy idea. I think my mom's problem with my son and previously my brother was not knowing how to deal with all that energy, it's easier to just give in to whatever they want. She is so adoring of him can't stand the thought of saying "no" :) But I bet telling her to give him something else to do will work for us, he loves praise and to "help" so that should be a good technique. I'm also thinking that reminding her of my brother's tantrums that lasted until he was 8 or 9 will help! :D
As far as giving advice to your daughter, I totally agree with the "my house, my rules." But that's a tough situation when you are at her house.