I haven't looked back on your history, but she's probably had these moments or periods of seeming normalcy before. As I recall someone(s) saying in the past, both these behaviors are her, she's not one or the other. Cooperation is her, however briefly, when she has to or when she wants something. Positive consistency is not her. Amazing how much we want to be wrong and surprised, isn't it?
She has definitely had periods of seeming normalcy before when nothing was going on, and we were all just trucking along. But this is actually above and beyond "normalcy"--she is taking initiative to be cooperative when usually, in her periods of "normalcy", she is just responding to DH's initiative to be cooperative.
Her fear of losing DSD is probably what was increasing her alienating behaviors in the first place. Now she is getting called on being an alienating parent and maybe being told she will lose DSD by doing that so she will allow the counseling for now... .my bet is when she gets scared of losing DSD through the reunification counseling again, she will be right back at acting out again.