Jenna is likely the main character in the story. She could be a young girl, a teenager, or even an adult. Since the story is named after her and the black cat, she's probably the one whose experiences are central to the plot.
As we don't have much information about this specific story, Jenna could be a protagonist who is a slave. She might be a symbol of the resilience of slaves in the face of the cruel institution of slavery.
The key is to find common ground. For example, both shows deal with the supernatural. So, a plot where a powerful supernatural entity threatens both the world of Supernatural and Mystic Falls would bring the characters together. Sam's knowledge of lore could combine with Bonnie's magic skills to fight this entity.
I don't know what you want to know about Jenna's novel. Please provide more background and context information so that I can better answer your questions.
I really like 'Klaus and the Unlikely Companion'. In this fanfiction, the OC is a witch who crosses paths with Klaus. What makes it stand out is the way it portrays Klaus's vulnerability around the OC. It shows a different side of him that we don't often see in the show. The plot twists are also quite engaging.