The music therapist is sure that she can find a way to reinforce an appropriate behavior so that it would?

incompatible. Its called Differential Reinforcement of Incompatible Behavior (DRI). Example, you reinforce her everytime she says something appropriate to someone, or sings, or has her mouth closed. The idea being, it is impossible to call someone a name when you are already saying something else, singing, or when your mouth is closed.