Delivering rounds on target is more critical than “stopping power”.
And recoil or the fear of recoil is one of the biggest reasons why many never are able to develop that required accuracy.
I’ve seen it time and time again at the gun club and across all types of shooters and guns. But especially with a new shooter and a female shooter, I would put recoil as THE consideration and I would consider only the lowest recoiling cartridge options like the 380.
Also keeping in mind that everything changes about a given cartridge when you put it in a super-light, super-compact CC handgun. Out of a full size, full weight pistol, the 9 MM has only modest recoil IMO. But shoot it out of a small-grip, super compact and it can buck like a mule.
One last thought. Guns are a LOT easier to change than are bad shooting habits like recoil flinching. It is far better to go with a lighter recoil level with the idea that she can change the gun later if desired.
Grouse