In the latest translated chapter, it was stated that it was possible for an avatar to escape the control of their main body.
I don't know if the avatar in question is a special case or not (it isn't an avatar of the goddess at least), but I still decided to assume for now that all avatars can become rogue.
Also, during a few seconds during which Ruphas was fully unleached (and during which she had enough power to casually destroy the solar system), Ruphas stated that she had predicted that she would be sealed and that Ophiuchus was moving in the shadow to help her. And she talked of Ophiuchus as a she.
Finally, when the Goddess gave her power to someone so that they could at least kill the Twelve Stars, Dina did something that obviously went against the Goddess's will to help Ruphas.