Где вы видели ревность к успевающим лучше её?В каноне такого не припомню,если вы о учебнике принца,то там её бесил сам факт жульничества.

Given that Mafalda was to be a nosy, loose-tongued girl, her canon role was to have listened in on the conversations held between the children of Death Eaters in her House. She then would have repeated this information to Harry Potter, Ron Weasley and Hermione Granger, hoping to wow them. Hermione would have discovered that, much to her own horror, Mafalda was her equal in many ways, and would have been caught between hating Mafalda's disregard for rules and longing to try to outdo her.