I kinda have this headcanon that a little bit after she got her cutie mark, Pinkie and her family visited Ponyville which Pinkie fell in love with. There, she encountered Buttercup who became amused by this cutie bundle of sunshine excitedly exclaiming how they both have curly hair. Having forgotten to ask for her name, Pinkie would only realize who Buttercup was years later as the mother of one of her best friends.