"If she was missing school and the parents were notified but did nothing to correct the absences, were they at least partially culpable for the dysfunction?"

Wasn't that the point the law that the teenager championed? To prevent school districts from blaming parents when the districts fail to do their job?  The parents appear to have done their due diligence: They approached the school before enrolling their child; they sought help from school personnel and then district administrators; and, finally, they filed a complaint with the state department of ed.  Would you make this same accusation if the student couldn't attend school because she was in a wheelchair and there was no ramp? Clearly, she needed accommodations, including an IEP, and the district ignored her; how is that her parents' fault?