Attagirl

Attagirl is the female version of attaboy, a compliment meant to encourage someone on a job well done. Adults, most likely parents, often use it to encourage a child when they're proud of their accomplishment, whether it be in sports, academics, hobbies, etc. However, people may use it in other contexts, such as complimenting a co-worker's or classmate's work.

Origin of attagirl

Attagirl evolved from the term "attaboy," which originated from baseball in the early 20th century. While attaboy is the shortened version of "that's the boy," attagirl comes from the quickened "that's the girl."