I second the vote for a revolver for a person who will have minimal training to begin with. Later on she can "upgrade" to a better weapon if she wants to.
Make sure she gets additional training and if your state allows CCW have her go through the course even if she has no intention of carrying. Good info in a course like that including the times when not to shoot.
Caliber is another personal thing. Just like you can't miss fast enough to win a fight, you also can't incapacitate what you cannot hit. I think a hit with a small caliber is far more effective than a miss with a .50 desert eagle. If she can hit with it go with the best cartidge possible but she MUST be able to hit with it.
If she is not likely to use it when she will need to, don't get her one. She'll just end up giving it to the person who should not have it. Most important rule to surviving a knife or gunfight is to have a gun. Second most important rule is to use it when you need to.
