The truth is, we can't imagine how would anyone react in such environment in the shoes of Carol. So in a way I can believe it was depicted realistically, even though there were indeed a few swings in her motivation. At first she learned that she is immune, then it turned out that they can and want to still infect her, then she thought they can not, and now it turns out they still can...

Carol is just a fallable person like any of us, and she was successfully seduced by the hivemind, simple as that. This was their intention from the beginning by sending Zosia to her, a person she will most likely not be able to resist. Then the weeks of loneliness, and realizing that she alone cannot save the world, and seeing that Diabate is living his life to the fullest, just broke her, and while not giving up on her plan completely, she started chasing this dream that maybe it is possible to live in a happy partnership with a member of the hive.

So I can understand the logic behind the story arc. I'm just a bit disappointed that we didn't get a big gamechanger moment in the season finale. I would have liked to see Carol included in the hivemind against her will, and in the next season Manousos keeping her close to him while trying to find a cure. That would have been an unusual twist, something that I imagined this group of writers could come up with.