Jean Webster 
Just Patty 

Patty and her two best friends Conny and Priscilla are appalled when they find out they’ve been separated as roommates for their senior year at Saint Ursula’s boarding school. Patty will not let it stand and the girls come up with schemes to go back to rooming with one another. The book follows Conny, Priscilla, Patty and their schoolmates (but mostly Patty) through their senior year. It’s a series of vignettes about friendship, mischief and growing up in the early 1900s. (Goodreads)