My first instinct would be to whack her sharply across the nose, but that isn't a good idea. She will just think you are butting her back. A better suggestion is to take a spray bottle with you and squirt her in the face when she tries butting you. Goats hate getting wet.
but I did it for a reason, we are going Nubian! I have my 2 doelings, today I'm off to by a buckling. Here's his pic