My first impression would be to get a .357 loaded with .38spl. She will not only have room to upgrade once she gets more comfortable with the gun, but the added weight of the .357 (depending on what you get, of course) can help with recoil a bit.
But the more I think about it, a double action auto like a Glock or XD in 9mm might be the better choice. They're as simple to use as a revolver (simpler, if she gets used to cocking the revolver before shooting) and gives a few more rounds capacity, which might make the difference if she panics and lets loose a few errant rounds.
I think the advice to find something she's most comfortable with is the best. A .44mag would be great, but if she's afraid to shoot it it's only a club that can be taken away and used on her.