In Binding Theory, Principle B says a pronoun must be free in its binding domain. But I wonder if there are any other constraints? For example, "He says her is great". In this way, "her" is free in binding domain but it is still not grammatical, is it?
Binding Theory deals with which pronouns can go where, but not which form of a pronoun you use. Case Assignment is what determines "she" vs. "her", and the position of the pronoun in "He says she/*her is great", the "she" form (subject/nominative case) can go there, but the "her" form (object/oblique) cannot.