What is the point in even having the Old Testament if you discard it? Christ sure used it a lot as well as NT Prophets and Apostles, so where does she get it that it does not apply?
While out of the Old Testament, this is a better scripture than Amos 3:7 on the subject:
Ex. 4:16 And he shall be thy spokesman unto the people: and he shall be, [even] he shall be to thee instead of a mouth, and thou [Moses] shalt be to him instead of God.
I think your best bet would be to show the fallacy of ignoring the Old Testament.