From the Super Mario Wiki
Pearl is an elderly woman living in Flipside during the events of Super Paper Mario. She is very kind to her naïve granddaughter and spends her time giving advice to Betsy who usually misinterprets the advice. She has a dark past in Flipside where she was once called Razor Pearl. She has many stories to tell, but most stories she cannot talk about. Her Flopside counterpart is also named after a precious gem: Ruby.