Perhaps you shouldn't supervise if you are not comfortable doing so; however, this does give you an opportunity to divide duties a little more than they are now. You say that you are usually swamped and the other position is not so swamped. Maybe before the person is ever hired, you could sit down with your supervisor and rearrange the job duties of your position and the one that's open.
Or, maybe you do want to supervise so you can delegate tasks to the other individual. That way there is a clear understanding that you can assign her work if she has nothing to do at that particular moment.
You need to feel comfortable being the supervisor, though. If you are not, then don't let anyone talk you in to it.
I agree that cross-training is essential in any position. You should always have back up.
Good luck!
Marcie
