Note that the instructor is vigorously opposed to any self-defense caliber less than 38 Special in a revolver and 9mm in a pistol. In other words, SUBJECT TO YOUR COMMENTS, 380 ACP is probably not being considered.
Frankly, it's a shame that the instructor was so anti-380 and probably filled your wife's head with a bunch of bologna horror stories about the inadequacy of the 380 ACP cartridge. Judging by what you have described, it sounds to me as if a pocket-sized 380 could be the perfect solution for your wife.
I have posted about this recently on a few other threads, but I'll repeat it here: my wife and I recently purchased a Kahr P380 for her, and it is a FANTASTIC weapon. The trigger is smooth and light, but not too light. Recoil is modest and manageable, even with defense-quality ammunition, and the pistol is comfortable to hold and "points" naturally. The pistol is slim, light (under 12 ounces), compact, and can be carried on one's person relatively easily, even under the typically form-fitting clothes of a woman. My wife took it to the range to test it out, and, brand new, the pistol had one stovepipe on the second round, and then 198 problem-free shots. By the way, Kahr warns that its pistols need a 200-round "break in" period. As she shot away in the lane next to me, I kept waiting for the string of failures, but they never came. If you can't tell from my description, I was exceedingly impressed.
Of course, everyone knows that, when it's come to "power", the 380 ACP cartridge is not a 45 ACP, but neither is the .38 Special a .44 Magnum. It's all a matter of compromise. If your wife finds the weapon manageable, possibly even mildly enjoyable, to shoot, then she will be willing to practice with it. If she practices, she is more likely to hit what she's aiming at, should she be in a situation in which hitting the target is of utmost importance. If the weapon is small and light enough, she will have it on her if she needs it. The bottomline is that it's unwise to purchase a weapon for her with which she is not comfortable, or can't or won't get comfortable due to trigger weight or recoil or whatever reason. I'd rather my wife have a sharp stick than her bare hands, and I'd rather she have a 380 ACP than a sharp stick, but, whatever she has, I want her to feel comfortable, competent, and proficient with it, and I want her to have it on her (not in a purse or locked up at home) should she need it. I want her to be able to use the weapon with confidence.
In addition, the horror stories about the 380 ACP catridge that I mentioned above are a load of hooey. Any "dud" catridge of any caliber will show unrepresentative perfomance. But, 99.999% of cartridges produced by reputable manufacturers are not duds, and any reasonably logical person will acknowledge that a 90-grain projectile travelling at 900 feet per second is going to punch a hole in just about anything not made of rock or a hard metal. The physics of it are undeniable. If one has doubts or questions about adequate penetration, good-quality FMJ or TMJ ammunition provides the answer.
Yes, yes, I know that an attacker may not be "stopped" quite as quickly with a 380-sized hole than a 45-sized hole, or whatever ammunition one wants to hold up for comparison. But, in just about any threatening situation that my paranoid imagination can produce, the appearance of a pistol in the hand of the potential victim is a game changer (as one poster alluded to above), and three or four shots are a game ender, whether the game ends with an attacker in retreat or an attacker who needs immediate medical attention.
In sum, as suggested by others, I would recommend reducing concern about caliber and increasing concern about finding a weapon with which she will become proficient and comfortable. If you have two or three choices with which she will become proficient and comfortable, choose the largest caliber of the bunch. Finally, do not rule out the 380 ACP. Regardless of the instructor's biases, the pocket-sized 380 ACP is a nice compromise between power, portability, and concealability. Prior to our recent purchase, even my wife scoffed a bit about the "weak" 380 ACP, but she's since changed her tune.