To Kill A Mocking Bird

The part that I am confused about is why Scouts teacher Miss Caroline Fisher is so aggravated that Scout knows how to read. She claims that she was not taught the correct way but when Scout was reading it seemed to me that she did just fine. The teacher should be happy that she has such a bright student rather then one who does not care about their studies. Is it really a crime that she reads with her father, or that she already knows how to write?