So, let me get this straight.
She loves shooting big guns. I mean, REALLY big guns. She wants to make sure her gun is powerful enough. And YOU are trying to talk her into a .380?
Seriously man, you sound like the stereotypical worst gun store clerk on the planet.
No, she probably won't carry a .50. But there is no reason on this planet she couldn't carry a .45. Holsters, concealment, training, etc, all of these things will be things to worry about no matter what gun she chooses, and YOU decide to handicap her options. There are MANY good compact options in ALL good defensive calibers to choose from. The only time I have ever conceded that a .380 is the best choice, is for my 65 year old mother, who has a wrist injury and arthritis, and she can't grip the slide well enough to rack normal guns. For anyone in good health, they can handle a regular gun.
I won't even start on my problems with the cartridge itself, but realize, smaller guns are NOT easier to shoot. They have a smaller sight radius, making them harder to aim, and less weight to soak up recoil. Let her look at a j-frame, a G-19, a Kahr, an XD compact, an M&P compact, etc. I would say to send her to the store BY HERSELF, but I know full well, many store guys will make the exact same mistakes you are making here.