I honestly recommended BJJ. IMHO, if a woman is genuinely interested in being able to defend herself in regrettably plausible scenarios, BJJ is the best choice. That style excels at subduing a 1-on-1 attacker where size/strength differential is almost irrelevant (at least within reason). You get stuck in a rear naked choke, I don't care if you're a foot taller and 150# bigger, you're taking a nap.

But her interest was more in fitness, sport, and the art of it. And I'll admit the logistics of us training at the same place is very convenient. Is TKD going to be supremely useful in a genuine fight? Eh, probably not. But I can confidently say she wouldn't panic, she would know how to defend herself, and she's also a whole lot stronger than she looks. She's smart enough to never try to throw any of the fancy aerial kicks that get you lots of points in a tournament because they leave you horribly exposed and unbalanced if you miss. But she's well aware that a quick palm heel to the face will stop just about anyone in their tracks.

All that aside, true self-defense is much more about situational awareness and avoiding/fleeing/de-escalating circumstances before they degenerate to violence. Sure, it's good to be able to handle yourself if a fight breaks out. But the truly enlightened soul goes to great lengths to not be there if a fight breaks out.