> She denies authorship of a report on the church fire, despite pressure from the other defendants, but then admits it rather than complying with a demand to provide a handwriting sample.... she is illiterate and has concealed it her whole life. The other female guards who claim she wrote the report are lying to place responsibility on Hanna. [wikipedia][1]

 So, she said she was guilty (even though she wasn't) only not to write down something, because she wasn't able. The whole life she's too ashamed of this thing so she never admitted, even if admitting it would have saved her from prison.


  [1]: http://en.wikipedia.org/wiki/The_Reader_%282008_film%29