Miyasaki was a happy and self-confident girl, until her father got possesed. She thought he had just changed and did more for his work, but it still changed her, too. She became very unsure and lonly, because the kids at her school didn't like her, because of her strange new toy, her changed dad had given to her. After he was normal again, she changed back, too.
You only get to know a small part of Miyasaki life, because Maron / Jeanne only meets her once or twice, at least in the manga. The first time they met, was after school, when Miyasaki ran into Maron, because she was trying to get away from to class-mates, who had made fun of her and her strange new toy, the called "weapon". Maron helped the little girl and cheered her up a little.
Of course she recognized her, when she had to "work" same night as Kaitou Jeanne and met Miyasaki and her dad. He had build up toy weapons to fight the art thief, but with a little help of Sinbad, Jeanne defeated him. After that Mr. Hiromi turned back to normal and so did the relationship with his daughter, and the small Miyaski herself.