Recipe for Love — Kara Lynn Russell

Roberta Pennybrooke didn't mind being the plain sister. After all, she had her studies and her secret correspondence with a handsome poet to keep her happy. But then Berta's beautiful younger sister comes to London for her first season, making Berta discontent with her unmarried state. Worse, Berta's poet writes to say that he is coming to London and wants to meet her in person! Suddenly she is desperate to change from ugly duckling to dazzling swan.