Just before this past Thanksgiving, I got to dryfire a really nifty S&W 686 (with maybe a 5" or longer barrel). What impressed me about it was the short, easy and incredibly smooth trigger pull -- single-action than the usual double-action found on revolvers. I think it's a Performance Center model. Nifty gun. Much funner to dryfire than my non-lock S&W 642.
Still if she's like most women, she'll want to be accurate. If she's small, it might be best to get her to learn with a handgun she can control and gain confidence with in a short time. A .22LR pistol would be a good starter pistol. Whichever model fits her hand and that she likes should be the one she gets. Since .22s don't have much recoil, a .22LR that she picked out and trained on may well inspire her to try a bigger caliber pistol. Honestly between a 9mm and a .40, for a second pistol I think she'd be happier with a .40 in terms of learning to tame her fear of firing a higher caliber pistol. Or she could do what I did -- go to a 1911 in .45.
And I loved shooting the Sig P239 .40. Great pistol.
"Let those find fault whose wit's so very small,
They've need to show that they can think at all;
Errors, like straws, upon the surface flow;
He who would search for pearls, must dive below." -- John Dryden