Gwendoline Christie’s character in the Star Wars sequel trilogy, Captain Phasma, was originally planned to have less screen time in Star Wars: The Force Awakens.
The comic book miniseries Star Wars: Captain Phasma is set after the events of The Force Awakens and explains how she escaped from the Starkiller Base.
All of these players will be returning in Star Wars: The Last Jedi next month.
Her backstory was explored in Phasma, a novel by Delilah S. Dawson as part of the Journey to The Last Jedi series.