I know she's too young to be a trainer and that Clemont is the one who caught Dedenne, but he caught it so Bonnie could take care of it, and she's actually the only one who takes care of Dedenne. Now, maybe Clemont's not helping Bonnie out because she may not want him to, or because he may want to see just how responsible she can be taking of Dedenne all by herself, but nonetheless, Bonnie is the only one who takes care of Dedenne. Also, Dedenne is never inside it's Pokeball, it's always carried around in Bonnie's bag. In the episode "A Jolting Switcheroo" when Bonnie accidentally took another girl's bag that had a Pichu in it, she became really worried when she couldn't find Dedenne, and while the others may have been worried as well, they never really panicked or anything like that, whereas Bonnie began to cry while searching for Dedenne because she was sad and a little disappointed in herself for losing track of Dedenne. Once Dedenne was reunited with Bonnie she began to cry again as she apologized to it for losing it. These two have a very strong relationship and Dedenne is hardly seen being used in battle by Clemont, and Clemont never asks Bonnie if he can borrow Dedenne even just for a little while, so with the exception of "A Jolting Switcheroo" Dedenne is always with Bonnie and not with anyone else.