At the beginning of Charlotte, I thought that the way Ayumi’s overly positive attitude, when seemed kinda disconnected from reality was due to Yuu’s treatment. He kept lying to her for his own convenience, never telling her he didn’t actually like pizza sauce anymore, for example.
But I guess I was wrong. That’s just how Ayumi is. She’s always smiling happily in any situation, unless it’s a situation where her life is in immediate danger.