Deep breathe....
How long have you had her?
Are the parents aware that she cries a lot?
Where do you nap her? She needs to learn to nap well, and I bet the rest would come together.
Personally, I would have a "tough love" conversation before terming. They need to work with you on getting her to eat on your dc schedule, have a predictable routine, and go to sleep independently. If they are willing to do at home what you MUST do at daycare, then I'd give it two more weeks. If they are not, then you will need to ask them to make other childcare arrangements.
What conversations have you had with them about this?