After the new story, Rowling reveals her personal thoughts on the character and how the malicious pink-loving witch was based on a real person that she knew. Although she makes sure she doesn’t reveal who that person actually was.

In the new musings, she writes:

Once, long ago, I took instruction in a certain skill or subject (I am being vague as vague can be, for reasons that are about to become obvious), and in doing so, came into contact with a teacher or instructor whom I disliked intensely on sight.

The woman in question returned my antipathy with interest. Why we took against each other so instantly, heartily and (on my side, at least) irrationally, I honestly cannot say.

But hastens to add:

This woman was NOT ‘the real Dolores Umbridge’. She did not look like a toad, she was never sadistic or vicious to me or anyone else, and I never heard her express a single view in common with Umbridge (indeed, I never knew her well enough to know much about her views or preferences, which makes my dislike of her even less justifiable). However, it is true to say that I borrowed from her, then grossly exaggerated…