I should say, it also happened to my mom with my sister. My sister is simply named after Mom, but at that time a certain doll appeared on the market that went sky high, and more of the name turned up. Never mind my mom was just irked that the "pet name" version meant her daughter would be tied in with same doll. And as it turned out, she really DID represent the beautiful, blonde thin fashionable girl too well.
So, I assume that your sister's name isn't "Cabbage Patch"?
Your sister's name is Chatty Cathy? ;)