She gave the rocket back to the kid.
She abandoned her mother when she was days from giving birth, all alone.
She was going to abandon the brother, causing him run and fall, almost drowning in corn. This ultimately lead to the father's death.
Not always mindful of the consequences. Impulsive, irresponsible, a little self-absorbed. So ... she's a teenager?
In all fairness emptying out those batteries should've made the toy safe. And the mother also went into labor several weeks prematurely. Plus the girl figured out the key to defeating the evil aliens - I'd say that earns her a little slack.
Okay, I went back and found that part. At the 26 minute mark you see the mother recording her blood pressure and heart rate readings (doing her own prenatal monitoring) on an October calendar. The square she's filling in is for the third. Then they scroll down and you see the 23rd marked "DUE DATE". Three weeks away. The father wouldn't have gone off with his son if he expected his wife was about to give birth. Probably why he took the kid out there though; when the new baby came, some of his father's responsibilities - like the fish traps - were going to have to fall on him.