And bah, Rumia's outfit hasn't been altered at all to indicate which Job she is. ...Unless she's been made a main character like Prishe or Aphmau. *shudder*
If I can get past my distaste for calling a canon character that isn't a blatant self-insertion on the creator's part a Mary Sue, I'd still say Prishe isn't one, as I didn't find her to be perfect or unsympathetic. There's no lack of main characters in fiction who are more intelligent or skilled than the reader/audience, but have managed to win popular support regardless.
To directly answer your question, if she were a Mary Sue "like" Prishe, I think she'd have greater character depth than she currently has, so, yes.