I agree with those posters who say that kids that age often have a hard time dealing with abstract issues. (Not all, mind you, some 13 year-olds are frightfully perceptive, and that’s what makes teaching them so hard because the levels vary tremendously.)
I remember teaching “confirmation” class to a bunch of 14 year-olds and we were supposed to have a discussion of ethics. The kids read a story and were supposed to evaluate the characters based on their actions. The story went something like this:
There are five people on a deserted island: Tom, Jack, George, John and Jane. Jane and John are a couple and they’re all friends. The island is actually two islands separated by a sound with a strong current, a bridge ties the two islands together. At one point there’s a storm that destroys the bridge while John and George are on one island and the other three are on the other. The separation of the two lovers is, of course, heartbreaking and they’re both desperate to get to each other. Luckily, Tom has a boat. Jane asks him to bring her over to the other island and he says he will, if she sleeps with him. Jane’s distraught, turns to Jack who shrugs and says it’s not his problem. Lots of back and forth and tears later, Jane sleeps with Tom and he lends her the boat. John’s thrilled to see her, she breaks down and tells him what happened. He gets pissed, calls her a whore and dumps her. She runs crying to George who immediately finds John and hits him. THE END
Now, this is a silly story, but what surprised me, and everyone else working with the kids, was that the kids were almost in universal agreement as to who had been the most and least ethical in their actions: Jack was the good guy because he hadn’t done anything and George was the bad guy because he hit someone and violence is always wrong.
The moral of this looooong story is that many kids that age have a very black and white view of the world and that influences how they analyze situations and themes. I agree that your student might not have read the whole book, but it’s also possible that in her mind leaving your family is always wrong, just like fighting, and the why and how is not yet important to her.
(We actually had some fun and slightly heated discussions about the island story among the teachers, I doubt I’ll ever forget the “Tom was just being a good capitalist” argument.)