I may try the contract. DD spent all morning ranting that I didn't buy the RIGHT snacks for her to take on her field trip today.

We had an identical incident to yours with the instrument, when DD was convinced she was supposed to already know how to play her brand-new violin, even without any instruction. She was hysterical and I had to snuggle her to sleep. I wasn't feeling as nice about it as you, though, it kind of made me angry she was being so unreasonable.