Not really DID/MPD/Schizo. When some actors or actresses play roles, they can get really attached to their characters (kind of like how Ryan Reynolds loved Deadpool so much that he stole the costume). Rin is just really attached to her characters to the point of making notes about their individual traits. The characters probably also feel really personal because she made them herself and that dumping the running gimmick between her and Eiji from before they were dating would be a waste (not to say that she can't move on from it but she doesn't want to yet).