If I was getting a gun for my daughter or wife I'd take her to a gun shop with a large variety of revolvers, and have her repeatedly pick them up and point them. Let her select the 2-3 that "feel good", then have her repeat the pick up and point drill, but this time aiming at something with eyes closed. Then open up the eyes and see which one is actually pointing at the target after the eyes are opened. The one that is pointing closest at the target when the eyes are opened is likely to be the most naturally pointing one in a stressful situation.
There are lots of anecdotal but consistent stories about wives at home pointing a gun at an intruder, closing their eyes and pulling the trigger until it quits going bang, and then when they open their eyes they see that they've put just about every round into the intruder because the gun pointed well. Not saying any particular person (wife/daughter/husband/son/etc) or any gender is more or less likely to react and shoot that way, but a gun that points naturally is going to be more effective in a home defense situation. So get her a gun that points well in her hand, period.
And yea, revolver. Preferably DA only without an exposed hammer sticking out to catch on things.
.38 is a reasonable load too. Plenty of load options suitable for just about any level of skill and hand/wrist strength, and likely enough stopping power without being too hot to handle under stress.
If you still go with an auto, consider both 9mm and .40. The .40 has both more recoil and more stopping power, but the round size/shape is short so the gun grip is often as small as a 9mm grip. That may be an important consideration when getting a gun for someone with smaller hands.