I need help finding the name of a book. I read it when I was in the seventh grade, and that was a while ago. The only thing that I can really remember is that a girl finds out that she is a clone, or something. And her sister was afraid of water. So when she was little, her parents dunked her, trying to make her afraid too... but she turned out to love it. Im pretty sure her sister was into gymnastics.
Any help at all would be great. Thanks.

Maybe "Double Identity" by Margaret Peterson Haddix?