Warning This Section Does Contain Spoilers
The porcelain pig was not included in the inspectors notes and there is no mention of it from JWJ. This would tell me that JWJ doesn't know that the pig was put inside the envelope. It is blue and white. Seeing as the pig is blue, Heather's stationary is always blue, and she is constantly talking of water, I assume she is represented by the pig.
In a previous episode (four) we were given the Faustus print with the demon. On the back was the words in Latin "Non sequi aus. Sequitur. Canes ostendere veritas." loosely meaning "don't follow the swine, the dog shows the truth." If Heather is the pig, she must be leading us astray.