Can i report my car stolen in Texas if the person is hiding the car because she is not making her payments. now she has moved i have proof of ownership and a signed contract between us?

No.

Contracts and not making payments is a matter for the CIVIL courts.

Your car has not actually been stolen so no CRIMINAL offence has been committed and if you report it as stolen when you know it isn't, you will actually be committing a crime yourself.