This post should hit triple digit replys, lol.
Here's my $0. 02. Take her to a local shop and see what fits her hand comfortably, then go from there. Keep it simple if she chooses an auto, but make the caliber 9mm at the minimum and . 40 cal would be preferably in my book. If she chooses a wheelgun, and there's nothing wrong with that either, minimum cal. should be . 38 special and I would choose a . 357 as they make many in the same dimensions of the . 38 while giving you the ability to use the mags. if you choose and if she can handle the increased recoil. The . 357 wheel guns will also be able to digest a steady diet of +p . 38's and allow you to start her off with the very mild . 38 wadcutter loads, for practice.
Choose a good brand, regardless of the weapon. S+W, Ruger, Sig Sauer, Beretta, Glock all get the nod.
Have her take a class, if available, and choose a well made holster as well.
Scott W.