She Was Pretty (2015)

As a young girl, Hye Jin was impossibly cute and lived a comfortable life with her wealthy parents. Since entering her teens, both her looks and fortunes have drastically changed. She currently lives rent-free with a friend and is a part-time clerk at a convenience store. Out-of-the-blue, Sung Joon, her childhood friend, contacts her and suggests they meet. He is unaware that Hye Jin recently spotted him and knows how fit and handsome he had become. Not wanting to disappoint him, she insists her pretty best friend go in her place. What could go wrong?
After landing a full-time job, Hye Jin is surprised to find out that Sung Joon is her boss. To add insult to injury, he is treating her with nothing but disdain and contempt. This is not the friend she fondly remembers, so she goes about hiding her true identity from him.