Carolina was overjoyed that Dexter had been keeping an eye on her lately. He really didn't want to make Dexter too tired, just because he was always waiting for him in the hospital.
But he did realize that Dexter was only doing it for his own good. it seemed that Dexter had indeed begun to pay more attention to Carolina. Carolina itself is a woman that Dexter has only recently become aware of. Not because Dexter didn't care about Carolina before, but because he was slowly getting tired of chasing after Stella constantly.
It seems that Dexter really doesn't want him to waste his precious time teaching Stella again. Dexter, he realized why he used to have to constantly pursue something that was uncertain for him, just because he loved that woman.