It turns out that Dinky Doo is not Derpys daughter after all!

I was just watching Sisterhooves Social becuase I missed it yesterday, and at the social, you see Dinky Doo, with SEAFOAM! What is the meaning of this?! Is Dinky Doo NOT Derpys daughter? Is Seafoam ALSO Derpys daughter?! Or maybe Derpy couldnt compete becuase shes Dinkys mother, not sister, and let her go with Seafoam, who also didnt have sister?! WHATS GOING ON?!