Do you think that perhaps you are offering her too many choices?
I knwo that sounds kind of weird but sometimes with younger children, if they are given lots of choices - ie 3 choices of what to have, two choices of how to behave, three choices of how the pounishment for behviour will go etc etc then they can just feel they have lost control and it is too much to deal with and the only way they can feel in control again is to control the person responsible for the choices - ie you!
I know these days it is all, let the child have choice, free speech etc. But I really believe that often, they respond better too very limited choices so that they can clearly see what they are dealing with.
Sometimes IMO they need to know that it is just a no and there is no extended discussion, emapathy or anything, it is just plain no.