Do you have some kind of representative or liason who put you in the position? Someone who can advocate on behalf of the program that got you there? You have a limited schedule for a reason and that was agreed upon when you started. Do you have that in writing somewhere? She is trying to use you, which might be good if it was worthwhile experience, you were getting paid for your extra time, or you were seeing this as a future connection - and you had the time to do it.
Since none of that seems to be the case, you or the program manager or some other rep need to re-state the agreed upon plan for you to be there.