Is it normal for a 15 year old to tell her older sister everything?

I don't know, I mean, if people on facebook don't have their profiles on privacy setting, then they're allowing anyone to look at their profiles, so I don;t see much of a problem with it. If that's something that you're sister's can do and bond then that's good for them. I think that maybe they should stick to, at least, people they know, otherwise they seem kinda creepy. In that respect, I guess I agree with you, but if that's what they want to do, then that's their business.