I have an entirely unfounded theory on her situation.
I sometimes have an overactive imagination, and I daydreamed a whole scenario. In it, she was a pretty good kid who had a horrible home life. Her mom was a trainwreck and had a loser boyfriend/husband that may not have been WCJD's actual dad. Tired of their constant fighting (and possibly tired of the man hurting her in some way, be it physical, sexual or otherwise) WCJD decides to leave and not look back (hence the lack of items she took with her) it may have been a spur of the moment decision after having all she could take. WCJD knows someone at the Ellis prison unit, and decides that maybe she could talk to him to find out how to disappear from her home life for good, and or maybe find out who could rough up the loser boyfriend/stepdad. Her mom sends out the boyfriend/stepdad to find WJCD, or he takes it upon himself to do so. He tracks her down pretty quickly and the confrontation takes place, resulting in him accidentally killing her after beginning to get physical with her. He then tells WCJD's mother that he just couldn't find her.
To me, this story may explain why she was going to the prison unit, and why no one there recognized her. She may have been much younger the last time the person she knew saw her.
The thing that bothers me most is the bite. I keep thinking that the bite was part of a reaction from her assailant. I am wondering if maybe she bit him first, and he bit her back as a response. I also wonder if he bit her (on was on her back, right?) because maybe she incapacitated him with a kick to the privates and he used that as a last resort when she turned around to run/walk away.
All of this is speculation, at best.