Who is Emma Whitestone from Plum Island and what is their importance?

Emma is the lovely and naïve president of the local historical society, and John's love interest for a week. She was Tobin's lover until Tobin was done with her, and she collected antiques. She had a vast knowledge of local history, especially concerning Captain Kidd and his treasure. Emma is raped and then murdered by Tobin after her affair with John begins.