(New here, first post.)
I am an Oregon native, and while I think it's generally true that we are environmentally conscious, I don't think it's reasonable to assume that every citizen would be, especially not when under emotional stress. Whatever Terri's actions that day, it sounds as if her life had become difficult for her, and I can see driving for a while, music on, baby quiet, mulling thoughts (nefarious or just troubled). I've done it myself when feeling down, and felt the cost was worth the comfort. So I don't think her actions are unbelievable or even unlikely, except when considered in the context of the day's other events and coincidences.