Someone Like Lucy

"I wish that there was a girl my age that had Lucy's personality and that she was my best friend." This way, Lucy could remain twelve years old and Jon could still have someone just like her as a close friend. The stone glowed, granting his wish, but nothing happened. He supposed he expected a girl to just appear in his bedroom. But obviously something else had happened. Holding the stone, he said "I wish to know what my last wish did." His eyes went wide, as the answer to his question appeared in his mind. His wish didn't create a new girl, like he expected, but rather it took an eighteen year old girl who already existed and gave her Lucy's personality and then it made her Jon's best friend. But which girl was given Lucy's personality?