Make your corrections count and then don't let her get in position to try it again. You are at fault if it keeps happening because you aren't changing the way you are handling her.
And I agree with horses using heads with humans to move them, and have seen them also use their heads to move each other in a herd too, although it usually causes other horse to move simply by moving head, rarely will horse stand ground, as they know nip is coming.
And use your elbow to correct in neck, or your thumbnail in jaw when she moves head towards you. You are letting this happen over and over because you aren't stern enough and you aren't changing anything.
Horses make me a better person.