Or she is the ultimate villain built from character flaws without one redeeming quality?
closed as primarily opinion-based by Thunderforge, Paulie_D, Machavity, Ward, RichS Jul 9 '17 at 22:13
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Umbridge's profile (by JKR) on Pottermore offers some additional insight into her more admirable traits.
She's a powerful magical practitioner (or at least highly competent)
An accomplished witch, Dolores joined the Ministry of Magic directly after she left Hogwarts, taking a job as a lowly intern in the Improper Use of Magic Office.
She's thorough in her work
Dolores was judgemental, prejudiced and sadistic, although her conscientious attitude, her saccharine manner towards her superiors, and the ruthlessness and stealth with which she took credit for other people's work soon gained her advancement.
She's a hard worker and known to be ambitious
While they valued her hard work and ambition, those who got to know her best found it difficult to like her very much.