Tim,
I just went through this trying to delete a dummy provider. AC support made this recommendation and it worked beautifully. After transferring all of the departed's appointments, set her day-by-day time slots to "Off". In other words, in the Administrative section, choose her as the provider, then, instead of setting her appointment schedule for Monday for 8-4, click "off". Do this for every day of the week and she will disappear when you restart AC.
Leslie