It makes sense to me. Her personality was very flat and her sudden change of heart... it just didn't feel right. First she was all for kill the dragons even after that flight she was 'we have to tell you father' even when Hiccup said they would kill Toothless she argued it further and then she just gave up... Her loyalties are iffy, I feel. Like she was one of those people that only sticks around when it benefits her or when no one is around to see. I hope the second movie manages to cast her in a better light.