I can't add anything to what's already been said except that nobody has mentioned the way her belt in #3 causes her dress to puff out below it. That's not flattering and it's your responsibility as the photographer to look out for that kind of thing. I'm still learning that myself so it's one of the things I look for in other peoples shots.
Traveller's crop and edit (revised) shows that you ain't that bad. Be nice to your sister, she's pretty and has a lovely smile for the camera. :thumbup: