Piper Hipp is a Sim created by Grant Rodiek that can be downloaded on The Sims 3 exchange. She is roomies with Liam O'Dourke and Kim Kent. Despite the fact that in her biography it is stated that she has the Neat trait, she has no such trait. It might have been switched with Neurotic, because in the Trait list, Neat is just above Neurotic.
This character was made for promotional purposes and does not exist in the retail game. However, her household is available for download from the official website for The Sims 3.