Go for fit first.
Find a gun that fits her hand first.
Problem with many autos is that they are double stacked magazines which makes them fat. Find one with a single stack.
Consider starting her with a 22 cal first. This way she can go thru 3 to 5 thousand rounds to develop good shooting habits.
It is easy to shoot 2 to 300 rounds without breaking the wallet with a 22 cal.
Once she is comfortable with a 22, then you can get her a defense gun. Personally I wouldn't go with anything smaller than a 9mm.
There are pros and cons between the 40 and the 45, my personal preference is a 45, but that is me.
Revolvers are simple, just grab and go. The problem I see with revolvers is double action trigger pulls are extremely heavy and in panic situations, they lead to extreme jerking of guns which means missing targets at close range.
I can put 8 rounds into a target in under 3 seconds accurately with my 45.
For home defense I keep 10 round mags, don't care if they stick out of bottomof gun, so I have 11 rounds versus 6.
I would be lucky to get 6 rounds fired with a double action revolver in 3 seconds accurately.
Granted, some revolver shooters are really fast, especially the Cowboy action shooters, but that is not most people.
Hope this helps