I wouldn't agree on food thing at all. I cook using my ingredients and I would give the same food for all the kids in my care. How can I give jelly to 1 kid and not to the other one? That is not fair at all!
In terms of payment, if she already agreed and sign the contract she should abide. IF she wasn't happy with the payment she should have mentioned this at the interview. She seems like a difficult/bossy parent.