Who is Violante Ondariva from The Baron in the Trees and what is their importance?

Known as Viola to Cosimo, and as Sinforosa to the fruit thieves, Violante Ondariva is next door neighbor to the Piovasco family, growing up the apparent only child of wealthy, land-owning parents and doted on by a flurrying cloud of aunts. She first encounters Cosimo while playing alone as a little girl in her family's elaborate and exotic garden, and is taken away to boarding school before their friendship progresses very far at all. Before Cosimo, Viola spends time commanding, protecting, and flirting with a particular pair of fruit thieves Cosimo later befriends. Playing men off of one another is a pattern Viola continues to enjoy into young adulthood when she and Cosimo are reunited.