It appears she was just threatened and was possibly going to be beaten or tortured. She probably was taking to court and before they could deliver the judgement Dumbledore arrived.
Umbridge was ultimately rescued by Dumbledore, although she was
apparently left with a significant fear of centaurs afterwards,
reacting violently at even the sound of hoof-beats. How Dumbledore
managed to rescue her from the human-hating centaurs without suffering
any injury himself remained a mystery, though it is likely that
centaurs had respect for Albus, based on their salute at his funeral.
When she was rescued and in the Deathly Hallows she never really showed signs of sexual trauma on her physical or mental person.
The centaurs consider themselves better than humans(which is why they were angered when Firenze let Harry ride on his back). They were probably planning on treating her like they were going to treat Harry and Hermione. They would have probably considered themselves better than humans, so doing anything other than beating or torturing her would be unlikely.
As the centaurs turned on the children, Hermione protested, saying
that centaurs did not hurt foals (young humans) and that they meant no
harm, unlike Umbridge, and were not from the Ministry of Magic like
her. Hermione accidentally insulted the centaurs by saying that they
had wanted the centaurs to drive Umbridge off for them, as the
centaurs took this as wizards thinking that centaurs existed to do
The centaurs, deciding that they were arrogant wizards as well and
that Harry was not a foal but nearing manhood, prepared to attack them
but then Grawp, Rubeus Hagrid's Giant half-brother, arrived. The
centaurs attacked him instead, shooting him with arrows in the face.
Grawp chased away the centaurs, howling with pain, as blood from his
face poured down on Harry and Hermione.
I agree that she was probably protected from the worse, because Hogwarts was associated with Dumbledore(and they respected Dumbledore) and because Grawp was causing trouble.
Umbridge was ultimately rescued by Dumbledore, although she was apparently left with a significant fear of centaurs afterwards,
reacting violently at even the sound of hoof-beats. How Dumbledore managed to rescue her from the human-hating centaurs without suffering any injury himself remained a mystery, though it is
likely that centaurs had respect for Albus, based on their salute at
Things that might have happened to her.
She could have had what happened they threatened to do to Harry and Hermione. But nothing that violates their code.
Whatever they did was probably was interfered with by Grawp (at least slightly)and by the fact that they respect Dumbledore and the fact that they consider Centaurs better than humans, it probably wasn't sexual.
"Over the plunging, many-coloured backs and heads of the centaurs Harry saw Umbridge being borne away through the trees by Bane, still screaming nonstop; her voice grew fainter and fainter until they could no longer hear it over the trampling of hooves surrounding them."
—Description of Dolores Umbridge being dragged away by the centaurs
People in this discussion seem to think that what happened to her was sexual,becuase of the mythology behind Centaurs. I however think that the mythology differs from books and other literature and the centaurs obviously don't like dealing with humans from what they did with Firenze(because he dealt with humans), they are bitter from the way they are treated.
My thoughts on the cracked article
They didn't mention any canon references to Centaurs acting like this in any other HP literature. They even mentioned this: Also, they never mention the "brutal nature of Centaurs" from the novels or movies in general.
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.
Why would she look unscathed if someone much larger than her brutally did anything to her?
The actor stands 5'0 ft tall and let's say that Umbridge does too. The Centaurs were much larger than her, she wouldn't look unscathed. She probably just laid on the ground and shrank away every time they came close or said her name(or threatened her).
- Madame Pompfrey would have treated her for her wounds if anything exceptionally brutal had happened to her.
Madam Pompfrey says she's just in shock,' whispered Hermione.
Just in shock, means just a scare, in this case at least. Madame Pompfrey wouldn't be hiding somewhere if someone was hurt very badly, Pompfrey was angry at her, but she probably wouldn't have wished rape on her.
- Most of the Centaur info was non-canon and from other sources(non-HP). That's like saying the vampires from Twilight are like the vampires from Dracula, Blade or a fanfiction someone wrote.
Remember when the centaurs were threatening Harry and Hermione, did they ever mention that they would do anything remotely sexual? No.