Why should she be different than anyone else, different from any of us? Take her to the range with a variety of guns and see what she gravitates towards. Let her decide.
The biggest mistake guys make is deciding what their girlfriend or wife should get and or making suggestions of what they should get.
If she doesn’t like it, she won’t shoot it.
If it doesn’t fit her well, she won’t shoot it well.
The cartridge it fires is far less important than just having a defensive hand gun when it’s needed. Estimates are all over the place but the highest estimates average aaround 1.4 million defensive handgun uses per year.
Those estimates inevitably get reduced to figures around 40,000 per year in government published studies as that number conforms with data from police reports, etc.
The massive difference between those two numbers are that the vast majority of the time a defensive handgun is effective without ever being fired.
At the least intrusive and reportable level, having a handgun, and having the situational awareness that often goes with it frequently prevents an attack in the first place. For example the wood be victim with a concealed handgun sees the potential assailant at a distance and makes eye contact. That by itself removes the lament of surprise and is often sufficient for an assailant to choose a softer target. And, if the would be victim is not displaying the level of fear the assailant expects, that sets off red flags in smarter criminals who again seek a softer target. Those numbers are impossible to measure even with a survey as the potential victim never knows for sure if they were in fact targeted.
Beyond that if the assault progresses, the intended victim drawing the weapon is more often than not sufficient to put an assailant to flight as they really don’t want to get shot. In some cases the prospective victim doesn’t have time to complete the draw before the assailant flees. Research data consistently shows this account for 70-80% of survey reported defensive handgun uses.
None of those instances have a high likelihood hood of being reported to the police, particularly in jurisdictions that are even remotely anti-gun.
Then you have the cases where a firearm is fired. However only a fraction of those result in the assailant being hit before fleeing. I suspect many of them are not reported either.
In those cases where the assailant is hit, about half will flee or surrender rather than risk being shot again, even if the hit itself is not incapacitating. Most of those are probably reported and included in the 40,000 estimate.
Cartridge wise, and magazine capacity wise, that leaves a very small percentage of defensive handgun uses where cartridge or capacity matter at all. That percentage is probably under 5% of all defensive handgun uses, and in the vast majority of those 6 rounds is more than enough to resolve the situation.
And yet way too many people make defensive handgun decisions based on what is probably a 1% worst case scenario. There’s nothing really wrong with that, until you consider that many of those individuals stop carrying their duty sized pistol and two spare magazines on their bat belt due to back pain or other convenience related issues and up making that quick trip to the local stab and grab for a pint of ice cream unarmed.