Hi! I agree with you that slapping hands sends a very mixed message. My DS is 11 mos and sometimes pinches me when he is mad or frustrated. I firmly tell him "You are mad, but no pinching" Then I immediately put him down. Of course he cries then and I take him over to his toys and begin redirecting him to do something else. I then evaluate why he was upset in the first place and try to fix it. Is he bored, Is he hungry, does he need a change of scenery? Since he can't communicate his needs or understand why I am not letting him do something he wants that comes out in pinching (or hitting in your case). They can get very testy when they don't get their own way, can't they! I have started explaining to him, in simple terms, why he can't do something "You'll fall" "That's hot" and then I always redirect him to something he can do and I sit with him and praise him for doing that. Sometimes I just have to take him to a totally different room or out on a walk because he is so focused on doing the thing that he can't do (example, climbing up on the couch and then running off the edge!!!

) I am finding though, that he is understanding more and more every day and it is the coolest thing in the world that I am the one that gets to teach him! So I just take each pinch or hair pull in stride because I know that they are a part of the learning process. Hope this helps!
PS Oh and of COURSE they don't do it for the babysitter, right! They save up all the richest emotion for M-O-M! I think that is soooo completely normal. She is so attached to you, you are her world and she feels the strongest about everything with you.