Why did she suddenly become protective of the Hive?

She had always been protective of people and felt bad if they collapsed after she got angry. 40 days is quite a long time to be completely isolated and if Zosia hadn’t come back, Carol probably would have killed herself. Also, notice how she confronts Manousos with similar arguments she was initially confronted with by the other humans: “Have you even tried talking to them? You could learn a thing or two.” She wants to be the one who knows better than others even if that means switching sides depending on who she’s talking to.