First, I do not think the Glock is a good first gun. They are lighter due to the Polymer body and tend to recoil more. Anyt caliber higher than 9mm kicks hard. Not saying the Glock is not a good pistol ( i am looking for a Glock 34 myslef)
I would suggest going the .22 route. First, the ammunition is much much much, did I say, much cheaper. 500 rounds for $20 compared to $220-$240 for the same amount in 9mm. If she really enjoys shooting and sticks with it you can test out lots of guns and make an educated decision.
If you really want the higher caliber as home defense may be part of your equation then 9mm is the way to go. .40 and .45 are going to recoil to much for a new shooter. Plus the price of ammo is going to hurt you pocket.
I tested pretty much every 9mm in the marketplace and chose the CZ 75 SP-01. I also liked the S&W M&P full size.