Bulls***.
Give a Magic Marker to a 12-year old. Put on a large, old white t-shirt. Tell the kid to "attack" you with the Magic Marker. Try to evade his stabs and slashes and try to disarm him. Then count the number of dots and lines on your shirt and imagine what an adult could do. Yeah, you would have acted differently if it was a real self-defense encounter, but I think you get the message.
I'm not saying that you shouldn't practice your weapon skills, but the "a weapon will inevitably be absolutely useless at best if you don't have any training"-mindset many traditional martial artists have is just so ridiculous.
If you are determined to use te knife to defend your life, it's plain stupid to believe that it would do you more harm than good.
I agree that a pepper spray
in her pants pocket (or better yet, a belt holster) would be better than a knife in her purse. And a knife in her pocket or belt sheath would be even better. OC is a nice option, but definitely not a defensive concept you can trust in all circumstances. Some animals, drug users and drunk people are pretty much immune against pepper spray. And guess what, it's not unlikely that violent criminals happen to be intoxicated.
Yeah it would be easy to give her a nice pink Spyderco Dragonfly and tell her to cram it into her purse, buried beneath handkerchiefs, lipstick and Altoids where she probably won't get it out in time if she needs it. The realistic option is to educate her. Telling her that at least
some basic training (even half an hour just once is better than nothing) is in order and convince to carry the knife in a place she can easily access.
Man, I should really keep in mind that BFC is just not the right place to discuss realistic self-defense.