Has anybody ever seen the movie thirteen?

Spoiler alert! If you hadn't seen this movie, don't read anymore. I don't want to ruin anything for somebody, who hasn't seen this movie, but I had a few questions about this movie for the ones that seen it. How come in this movie, Tracy's mom Mel didn't want to adopt Evie? Remember when Evie always stayed at Tracy's house? I know Evie had somebody by the name of Brook, but she didn't want to stay with her? It seemed like she'd rather stay with Mel. DO anybody know why Evie wanted to stay with Tracy's mom?