THUS, you are best served in this case by getting her a cell phone and teaching her what to do if she gets lost. Preferably a cellphone that already has some of these features available.
I have implemented such a system myself for my company, although for vehicle location rather than people. We use off-the-shelf USB dongles on a laptop, and we have a client app on the laptop that "phones home" every few seconds with the updated positions. A server side app allows plotting points on the map (research Google Maps or Microsoft Virtual Earth). It's very neat, and I'm sure its exactly what you want for your daughter... but since you would want her carrying around a "small device" rather than a laptop anyway, you're looking at a cellphone.
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