Hard to find THE Answer, but there is a key factor.
GET HER TO STORES, RANGES, AND FRIENDS WITH LOTS OF GUNS. LET **HER** PICK. See anecdotes below.
That said, if the aim is for her to learn and enjoy shooting, with no immediate need for a personal weapon, I would show her a S&W M17 or M18; the old K-22 with 6" or 4" barrel, respectively. Later S&Ws are way heavy. Single action revolvers are harder to manage, in my opinion, but a Ruger Single Six is OK... get the adjustable sights.
I guess the worst thing about a revolver is the 12 lb DA. For target shooting only, thumb cocking gets her a nice 3 lb SA, though. Operation is simple, ammo selection is versatile. Price is lower for equal quality.
The best feature of an auto is its consistent trigger, unless you stick her with a DA/SA design. Fight a 15 lb recoil spring to cock and a 12 lb magazine spring to load, but only once per string. Ammo is critical. More rounds in the gun for gunfighting.
A .22 cal is best to learn on, cheap, quiet, and accurate. A .38 is ok if you handload or are willing to pay for target wadcutters that don't have much recoil or blast. A 9mm can be hard to work with, they are loud and have a sharp snap to the recoil.
I have worked with two novice women.
I started one out with a S&W M18 .22 revolver. She ended up preferring a M19 with Specials, shot ALL Double Action at any target, any size, any range. Autos, even .22, did not interest her.
The other I started with the same .22. I worked her up through .38 revolver which was ok, .22 auto which was too mild after shooting a centerfire, 9mm auto (Glock) which she found unpleasant, and finished up with a .45 which delighted her. Of course it was my elderly Pachymayr Special with powderpuff handloads as would be used for 50 ft target shooting. So accuracy was excellent, recoil no more than the .38 Special, and Great Big holes in the target. Holes amazingly close together for a beginner.
Her friend, slightly experienced in shooting, came to watch an IDPA match and visited the S&W demo range. She enjoyed blasting away with their .40s. She seemed to favor the head shot.
My chiropractress shoots a Colt Python with .38s for fun.
I know a lady with a Browning Buckmark and another with a Ruger Mk II. Racking the slide is a chore but if you handle it right, you only have to do it once a day.
Another is a top-notch Cowboy Action Shooter. She is a snake with a .38 Single Action, faster than me.
Gun choices are personality driven. Get her looking.