If she really wanted to learn to defend herself on the street, she would learn Krav Maga, but seeing as how that is an Israeli martial art, I’m guessing she won’t.
I would not like to exclusively rely on Krav Maga. If someone has a knife you may ge a last surprise. I used to think martial arts were good, but now I think a CCW pistol in the hands of a practiced shooter could take down Bruce Lee.