According to one of those silly tests on FaceBook, when it comes to Sesame Street, Fiorella is a Big Bird--naive as the day is long and far too trusting. The accusation is true. If you want to tell a whopping big lie, tell Fio. She'll believe you because you're her friend. And she'll back you to the hilt too because she's loyal as Greyfriars' Bobby.
All of this means that Fio gets burned at regular intervals, but she'd rather have it this way than be an Oscar the Grouch.