As a father to a girl (albeit she's only coming up to 3 years old) it's a concern that when she's older she's open to more risks of physical/sexual assault than my son. As a Taekwondo 3rd Dan black belt I've always said that my children will learn Taekwondo until black belt level (after which they can decide to continue or stop). However, I know that not everyone has the level of training to teach their children or the finances/opportunities to send them to a class.
In 2006, a young girl named Dallas Jessup made a movie called Just Yell Fire with the support of her local community and her Philipino Street Fighting coach Chad Von Dette. This movie has been released free of charge on the internet and can either be downloaded as a normal PC/Mac playable movie or as a DVD image for burning to a DVD and showing on TVs in school.
The video is a great production. It goes through a Dating Bill of Rights which, although very american sounding, is a great list of rights a girl should consider herself to have in any dating situation. It then goes through 10 techniques for self-defence in abduction situations.
The first two are excellent. The first is to bite your opponent. As it says in the video, children are conditioned from an early age to not bite people. However in an extreme situation where you are being abducted this is an amazingly effective technique. The second is to yell Fire at the top of your voice. The instructor in the video says that often Help is ignored as are screams (I know this from having lots of kids living near me, I often tend to ignore them as it's used when playing). Yelling fire gets more people's attention as a fire could potentially affect them.
They then go through a selection of techniques, some of which I doubt the effectiveness off (the hair comb release from a choke by a much larger attacker) and some of which I remember are banned from being taught in some countries (the ear slap), however as a collection they probably represent a good selection of simple techniques that could stop abductions.
I'd highly recommend the video to ALL parents of teenage girls, schools that could show the video to teenage girls and any martial arts instructors that are willing to teach this simple system as a short course.