First of all it's really annoying to loose a party member you have invested so much in over the course of the game without being able to do shit about it.
That is not exactly true. It is possible to get her to turn on her former master and keep her in your party.
I don't think it matters if you have the Obedient trait on your main characters. What matters is what you said to her during the dialogs your have had with her up to this point.