Elena is presented as a supporting character that's a POG and she's an idol that hosts the tv program "Puzzle Kingdom". She's very famous among all the people that are as followers for her, but not just for fans only: she's very appreciated from puzzle fanatics as Kaitou because usually, she's the person who design and projects all alone the puzzles that are used in her program.
Talking about her personality, she's a very selfish and manipulator kind of person, one that wants to be always the number one and doesn't want to be defeated by anyone. Her nickname is Antoinette, and I think that it fits almost perfectly to her, because she doesn't have any kind of mercy with anyone. Anyway, inside of her, she's a totally different kind of person: when she meets Gammon, she understands that the type of life that he lives is the one that she would love to have... a life full of friends. In fact, she doesn't have any, and she feels alone the most of the time she spent with just herself. Even if her personality doesn't allow her to tell the truth about this, everyone, especially Gammon, understand which is her main problem.
In a match, were Elena invites Kaitou to solve a puzzle made by her, she will put in danger not just his life, but the one of all his friends. And when, at the end, she will realize that she was the one who has been tricked, she will help them all to find a solution to the game. Kaitou will find her first book where she started to learn to make puzzles and to solve them. When she was a child, her mother wanted her to become important, but she wasn't particular in any kind of field. When she found out about puzzles, she wasn't good at all with them, at the begin, but realizing that in this way she attracted her mother attentions (and not just them) on her, she started to become almost obsessed with them, up to the moment in which she was the one who create them. At the end, she will understand in what she was wrong, and will continue to argue with Gammon until the end, even if in this case, it will be not for jealousy, but only to challenge him until she will win~