Another possibility is that she is a character from a different group that Rick's group encounters. She might initially be distrustful of Rick and his people, but over time, a relationship develops. This would create a story full of tension and growth as they have to overcome their differences and learn to trust each other in order to survive together.
She could also be a character who has a pre - apocalypse connection to Rick. Maybe they were old friends or neighbors who reunite in the chaos of the zombie - filled world. This would bring a sense of familiarity and history to their relationship within the fanfiction. For instance, they could have shared memories of their hometown that now serves as a source of comfort or motivation in the difficult times they face.