I've read Sophie's World - I checked it out and got it for a younger family member a few years ago. It does what it does very well - introduces some fundamental philosophical ideas and mechanisms for younger people, particularly girls, since 'Sophie' is herself a girl. It's definitely worth a look but I suspect it may be a bit too 'young' for you but, if you've got a 12-16 year old female family member with a few more watts burning in her head than the usual contemporary cultural mush, then it would likely be a good one to pass on.