I think Jeanne gets a little bit more growth than that. The part about this scene that made me start to tear up was after they talk about CalArts, and the conversation goes a bit like this:
Zach: "He (Cody) will be fine with us. Or stay, it's your choice."
Jeanne: "Zach... if this thing with Allen doesn't work out, it's best that he's here with you."
Zach: "... He's in good hands, I promise."
Jeanne: "... yeah..."
In the following embrace, Jeanne seems on the verge of crying. I think she begins to realize that Cody is her son, whom she gave life of her own life, and she DOES actually care about what happens to him even if she has been unable to take responsibility for raising him, and finally an acknowledgment of everything that Zach has done. And yet she decides to leave anyway, it makes it even sadder when we switch to see the three boys watching her drive off. I'd be willing to bet that if the camera had panned over to see the car driving away, we might have seen Jeanne looking wistfully back at them.
I don't think Jeanne ever cared for anyone but herself her tears when she left wasn't for her son. It was a act that should couldn't control Zach anymore. Zach woke up we saw what Jeanne did when she said Shaun was only using Zach. Zach was finally happy and was applying again to CALARTS that was what Zach mom wanted that was her dream was much as Zach's but that ruined Jeanne's plans why you think when he told Jeanne he was re applying she said again we cant do that. No one in my family has ever discouraged us from trying to better our selves she did cause she didn't want Zach too she wanted Zach to stay cause if he left she couldn't control him. Only Shaun believed in Zach and loved im IMO. Any any of you want fan stories their is a site fanfiction.net with shelter stories...