Knife fighting is up close and personal and it's a very nasty business. First and foremost, in my opinion you had better be a good fighter to begin with before thinking of using a knife, because remember, most likely you will have to "fight your way to your knife" before you can use it. Knives are very poor defensive weapons for those not trained to use them.
Excellent point Tolly. An attack will almost always be of the ambush/surprise
type, with enough force used in the initial attack to overpower the victim.
Also, there is always the possibility that the knife, if you manage to draw it,
would be taken away from you and used against you.
Most of all, try to teach her the importance of carrying herself with confidence and not looking like an easy victim. When it comes to human predators this can be one of the best ways to keep yourself out of harms way. Bad guys don't want to mess with someone who looks like they'll fight back when they're are plenty of others who look frail and meek.
Reconseed made a good statement in a similar thread in the Outdoor section.
To paraphrase him, he said that the most important tool is the one between
your ears.
Make sure that you are aware of your personal situation at all times.
Like you said Tolly, don't look like a victim. Look like you know how to take
care of yourself, and they will look for someone else to take on.
Oh, and if she listens to music while on her walks, get her to stop.
It's really amusing to me to see those people who walk around with earbuds and
MP3 players going. Whatever it is that they are listening to, only serves to
distract them from what is going on around them.
They loose their situational awareness and become vulnerable.
Why give someone else the advantage by disabling one of the senses (hearing)
that warn you of danger?