Rosalyn is a high-school senior and the only person who will babysit Calvin. She hates doing it, but gets good money because she has a monopoly on the market: no one else will babysit him.

Power over Calvin

Rosalyn is the only person Calvin really fears, though this doesn't stop him from being a brat; he tries to escape or kick Rosalyn out on almost every occasion. Rosalyn does not hesitate to fight back however. After her first meeting with Calvin, she now sends him to bed early and watches TV. Often her boyfriend Charlie will call, and Calvin will always get on the other line: "Say, Chas, don't you thing you're settling for too little in the girlfriend department?" Rosalyn was originally created as a one-time character, but Watterson decided to keep her due to her unique ability to intimidate Calvin.