I am a fan of Lahaina Divers. I would also mention that it will probably be easier for your wife to dive from a boat than from shore, and she can do a very easy entry and exit, donning and removing gear in the water if she wishes. If you want to go shore dive, there are some very user friendly sites where you are: Black Rock and Old Airport come to mind. You can hook up with any one of a number of instructors in the area through Lahaina Divers or other places mentioned in this thread.
Divemaster Dennis
Divemaster Dennis