@Crikey: Unless you live in a dangerous area, I think walking home in daylight is fine. It is a risk I myself would take. Apparently, your son's girlfriend can handle things just fine herself, which is good.
You driving her home would also be safer than your son walking her home. You trust your son, but another hypothetical boy she might date might not be so safe to be with, so from a purely statistical point of view, you are a safer person.
Statistically, her boyfriend is more likely to assault a girl than a random stranger.
What I always find about the 'let's tell women to be careful' brigade is that they're not very keen to say why women should be careful
Unwillingness to name male violence, it's an epidemic.
If you pay attention, it is really everywhere. I recently read a text about domestic violence. From a feminist source. "Women who experience domestic violence", "women who flee from domestic violence" ... the fact that "domestic violence is caused by men" was mentioned, but seriously, why not just say "men who beat up women" instead of making it sound like the domestic violence just happens to women like, say, a heart attack?