Being unfamiliar with Starfleet protocols, she had a hard time adjusting to life on Voyager.
She and three other former Maquis, Kenneth Dalby, Chell and Gerron, were selected by Commander Chakotay to participate in Lieutenant Tuvok's Starfleet Academy-style crash-course aimed at bringing former Maquis members unfamiliar with Starfleet up to date. Tuvok had her remove her "festive" headband, as it violated regulations.
During a simulated battle exercise, Dalby ordered her to fire at will and do as much damage as possible to Romulan Warbirds attacking them. As a result, she, along with all the others, "died". (VOY: "Learning Curve")
Henley was played by Catherine MacNeal.
According to the video game Star Trek: Starship Creator, Mariah Henley was born on Nuraka III to parents Loren and Donald Henley. She has a sister named Catherine.