Leila

Leila is a legionaire and an old comrade of Jason Grace. Her rank and cohort at Camp Jupiter are unknown, as is his immortal ancestry. She fought in the Second Demigod Civil War, led by Octavian, centurion of the First Cohort, and reluctantly by Praetor Reyna Avila Ramírez-Arellano.

History
Little is known about Leila's past. It can be inferred that she was trained at the Wolf House by the wolf goddess Lupa. At some point, she made his way south toward Camp Jupiter and was accepted into the legion by the augur.

Presumably, Leila fought in the Titan War, since Jason Grace considered her to be one of his old comrades. Whether or not, she fought in the Battle of Mount Othrys is unclear.

After the second fall of the Titans, Leila likely also fought in the attack on Camp Jupiter, alongside Reyna Avila Ramírez-Arellano and the new recruit Percy Jackson.

The House of Hades
After confronting the pirate Sciron, Jason fell into unconscious mid-air, dreaming about the Romans' gathering in New York before their planned attack on Camp Half-Blood. Jason recognized Leila among his old comrades, which also included Dakota, Nathan, and Marcus.

Leila was present when Rachel Dare arrived with Grover Underwood, as ambassadors from Camp Half-Blood. Rachel provided Reyna with a message from Annabeth Chase. Upon this, Reyna departed for Greece, reluctantly leaving Octavian in charge. As soon as Reyna was out of earshot, Octavian told Leila and the others that there were going to be some changes in the legion's plans.

Trivia

 * Leila is a variant of the Arabic name Layla, meaning "night."