And unfortunately, the ... um ... "equipment" to go with it.
People on the Internet familiar with the mythology were quick to notice this, as were feminist blogs. After all, showing Umbridge getting dragged away by centaurs would be like having Draco Malfoy getting his comeuppance by having him get hauled into the back of a windowless van by a creepy guy with a wispy mustache. We don't need to see what happens next if we know the context.
The thousand-yard stare of a woman who knows her centaurs.
Now, if that had been the last time we saw Umbridge in the series, then you could say, OK, maybe these centaurs are different, maybe they just trampled her to death or stabbed her or tied her to a tree and strapped a bag full of oats to her face. But Umbridge comes back, and comes back suffering from some kind of major trauma that didn't involve any damage to the visible parts of her body. Here's Rowling's depiction of her in the aftermath:
Professor Umbridge was lying in a bed opposite them, gazing up at the ceiling .... Since she had returned to the castle she had not, as far as any of them knew, uttered a single word. Nobody really knew what was wrong with her, either. Her usually neat mousy hair was very untidy and there were still bits of twigs and leaves in it, but otherwise she seemed to be quite unscathed.