I mean, if u so worried about her why didnt u worry when she was alone looking for someone to join? Kagami no baka.
Im not sure about Sheep-kun tho. His heart hurt because of her story? Thats quite unusual. Also forcing his friends to accept her in the group seemed kind of desperate. He did seemed to be telling the truth and would be too much to write a novel about amnesia just to get her attention. But the circumstances are still a bit fishy.