Donna Troy was rescued from a burning building as a young girl by Wonder Woman and taken in by the Amazons. Over time, she trains and becomes Diana's sidekick by the end of the film. 

Donna is just a side character in this film, but a character that will return in the future, whether it be in a sequel or spin-off (please bear this in mind if you're auditioning! This is a small role but a character that will return). She brings a sense of youth and idealistic optimism that isn't present within some of the other characters.