Twilight had put up one hell of a fight, but was eventually captured, subdued, and forced into a SecurU sack, which was then permanently locked shut. A magic inhibitor ring was slipped over her horn, and she was transported to a remote mountain in Equestria's north. Twilight feared that she was going to be incarcerated in a long-forgotten dungeon, a fear that came true when she was taken to a large, cavernous chamber in the heart of the mountain. There, she was shackled to a pillar, the locks then destroyed and welded shut. There, her captors then explained her fate: she would spend the rest of her life imprisoned here, doing what she always wanted.
Soldiers began to bring in shelf after shelf, and crate after crate jammed full of books.
Twilight's captors explained to her that, in light of her long and admirable dedication to Equestria, she would spend her incarceration not in quiet isolation, but in reading all the books she wanted (save anything that could help her escape). When she was done with one, another would be brought in, ensuring she would have a never-ending supply of stories to satisfy her curiosity.
Shocked, but delighted, Twilight squeed. She didn't even resist as a ballgag was buckled in to ensure her silence. A pedestal was presented, her first book put on it, and Equestria's leaders left, leaving Twilight to begin her sentence.
It wasn't long before Twilight was hopelessly addicted to reading her books. She went through hundreds every month, going through page after page, until she all-but-forgot about her bondage and the world outside the mountain. Her whole world was nothing but books, and she couldn't be happier.