The only key characters in arc 1 she's not responsible for are Mitama, Kanagi, Tsukuyo & Tsukasa, Mel, Kanae and Sakurako. All the other main characters for arc 1 are done by her, as well as the majority of arc 2 characters.

I think you might be confused, as Aoki Ume is the designer for the vast majority of Magia Record main characters.