Well you do have a few options, lots of good ones already posted. Just have a couple questions.

1. Is this person giving you the work, is she above, below or equal to you in seniority?

If she is equal or below, I dont see how she can pawn her work off on you, If she is above I guess thats another story!

2. Is she doing late night extra caricular activities with your manager?
This could explain why her work is getting pawned off onto you, in another department that has absolutely 0 to do with sales.

This may be something you want to discuss with your boss's boss
(assuming your boss has a boss). This also depends on if your company has an open door policy or not, the one I work for does, and its nice.. If my boss is being a dick I can talk to his boss.

Other than that you can always give everyone the One Finger Solute and walk out (make sure you have another job ofcourse).

Good luck.. and may the force be with you