Actually, I don't have a long essay to write here, since a little bit of googling showed that she was very, very wrong when she claimed that Kashmir has never been an integral part of India.
What did I hit upon? The Constitution of Jammu and Kashmir (yes, there is one, and it was adopted on 17/11/1956), which clearly states:
3. Relationship of the State with the Union of India:-The State of Jammu and Kashmir is and shall be an integral part of the Union of India.Quod erat demonstrandum. Arundhati Roy, may I ask you to please get your facts right?