Louisa "Lou" McNally was the 8-year-old foster child of the Papadakis family (in Book 62). She was described as having short, spiky hair slicked back on both sides, wearing a loose sweater & jeans. She is not very big for her age and it was hard to tell if she was a girl.

She doesn't like being called "Louisa." She has an older brother named Jay. Her father passed away and her mother left when Lou was only a baby. Her brother lived with another foster family. Lou's father taught her about Big Dipper & Orion and could hoot like an owl. She only remembers that her mother smelled good and was strong.

While living with the Papadakises, Lou took Linny's bike and rode it down the hill at the playground without using any hands; she poured brownie batter on Hannie's head while Dawn babysat them, and she stuffed Boo-Boo (the Thomas-Brewer's cat) in a pillowcase. Lou had a dog named Jingles, who ran away.

Lou and Jay go to live with their aunt & uncle (their father's brother), Mr. & Mrs. McNally, who are good with them. They give Lou a 3-month-old black female Labrador whom she names "Happy."

In Book 116, the McNallys move to Stoneybrook and when Abby babysits Lou & Jay, Lou appears polite & calm, and dresses more feminine. She starts acting perfect. Jay tells Abby at Lou is behaving this way because she's worried about being sent away if she isn't perfect, but her aunt & uncle assure her that it's not the case.