M.B.
I don't think she's lazy. It sounds to me like she is just trying to control the situation because she can and she doesn't want to do what you are telling her, she wants to do what she wants. Working out some kind of reward should give her the incentive to *choose* to go on the potty instead of to hold it. I've heard many parents and child-care professions say that if you push them, they will push back.
Good luck!