Calendar Girl by Georgia Beers

Addison Fairchild has been groomed her entire life to run a division of Fairchild Enterprises, and she takes that destiny seriously. Work is easier than dealing with people, especially when her employees dislike her, her best friend worries about her, and her dating life is a disaster. With the company about to choose a successor, Addison is desperate to prove herself, which makes the arrival of Katie Cooper a nightmare. Katie is cheerful, optimistic, and a morning person, and Addison cannot stand any of it. Katie, juggling bills and caring for her father with dementia, takes the assistant job out of necessity and immediately clashes with Addison. Forced to work together, they discover that their differences spark something unexpected, proving that opposites really can attract.