Barely Lethal (2015) online

Megan Walsh has been training to be an international assassin for Hardman. However while she is on a mission, she notices how other teenagers her age seem to be having fun and enjoying their lives. Desiring a normal life, she bails out of a mission and enrolls in a student exchange program, in the process, being adopted by a foster family. She soon becomes a part of the high school and is subjected to the pressures and life of being in this environment.