Who is Battista Piovasco from The Baron in the Trees and what is their importance?

Younger sister to the boys, Battista spends much of her childhood dressed as a nun and confined to the family home following an incident in which she makes an attempt on the virtue of a visiting family's son. To occupy her time, she tortures, kills and maliciously cooks and serves all manner of creatures, presenting arrangements of them, such as a lobster gripping the tongue of a pig, lying in the pig's open mouth as a tongue itself, and snails decapitated and their heads propped at the end of pieces of wire mesh in order to produce the appearance of swans. She prides herself on being the most shocking member of the family and is observably put out when Cosimo takes to the trees, surpassing her on the oddity scale. She marries and has a family, but retains her love for torturing small animals. She builds a reproduction of a French guillotine and decapitates rodents for small audiences.