My wife has her guns, I have mine. That said, the 4inch .357/.38 loaded with .38s for practice is they way to go. There is one challenge to all this though. If she is anyting like other women I shopped with, they like things shiney and new. Make and model matters little to most gals, but they must have one that looks good. I know many of us do not care if the finish is 100% or if there are rub marks from holster duty, but if it is to be HER gun, then she just might.
My wife like to go gun shopping, she looksk them over and picks out ones she likes. Then we talk about features. I like to make it a shopping expirience and fun for her. Don't bag on her for picking one you don't like, remember, it is her's. You can steer her away from things like the big 500s or 480s, but if she picks a nice .44mag, put .44 spls in it.
Once she has her gun picked, then training if she has never shot before. This will go along, long way.
Then, but equal to all others is practice, practice, practice. If she can't wake up at 3AM and bring her gun into service in less than 10 seconds, she needs more practice. She should be able to find it, load/unload it, and fully use it in the dark just getting startled from deep sleep. The only way to do this is practice and usage.
My wife hates shooting paper at the range, she will last all of 10 minutes before she is bored. She will however, shoot whistle pigs all day long and want to come back the next day for more. She likes to shoot milk jugs, soda bottles and anything that reacts to being hit. Find what yours likes, let her have fun so long as she is safe.
The only drawback to this approach is she will start dipping into your gun budget, mine started with her 10/22, now she has a Rem .22, Ruger 223, Single Six, S&W K38, and a Wing Master.
Have fun with it though, it can be somthing you both do together.