Young Wizards #3. Author: Diane Duane.
Young wizards Nita and Kit have a new problem: Nita’s sister. Dairine is too smart to be Nita’s little sister; she’s too smart, period. So, when the new family computer clones itself and suggests that Dairine go into New York, Nita and Kit find themselves acting as escorts. Somewhere in the Museum of Natural History, near the ladies room, there is a door. It doesn’t lead where it’s supposed to, it leads into outer space. (Goodreads Summary.)
Sexual content: Passing mention of Nita having gotten her first bra, developing, and having temporarily high levels of power from hormonal surge.
Language: 2 scatological terms, 1 damnable
Violence: One alien is destroyed, girl is chased across a dozen worlds by aliens, spoken fight with the Lone Power.