In the 'tracy thurman story', Tracy Thurman was a woman who was brutally abused by her partner. She was someone who had to endure a lot of pain and suffering due to domestic violence, and her case became a focal point for highlighting issues related to domestic violence protection.
I don't have enough information to say for sure. It could be fiction, or it could have roots in reality that have been adapted or exaggerated for a particular purpose.
In Sierra Vista, there was a story about a hiker who got lost in the nearby mountains. As night fell, he started seeing glowing eyes all around him. He felt like something was stalking him but couldn't see what it was. In Sacramento, there are stories of a cursed alley. People who walked through it at night often felt an overwhelming sense of dread and some even claimed to have been physically pushed by an unseen force.
In this fanfic, Tracy Davis could be an original character created by the author. She might be a witch who has her own story and reasons for being betrothed to Harry.