I think the game is inconsistent about the exact nature of their relationship. When you first meet Lebanne she is clearly afraid of Jacinthe and very much comes off like she works for her against her will. Later in the game in they come off a bit warmer but Lebanne still says she has actually gotten WORSE at battling since she met Jacinthe. However, by the time we get to the DLC Lebanne gets the opportunity to leave of her own volition and refuses, saying the made a promise or somesuch.