Another sad tragedy.  I can certainly sympathize with the family's grief, but it seems pretty clear what the problem was.  My respectful and civil question is what exactly does the family hope an inquiry will reveal about this tragedy?  There doesn't seem to be any mystery here.

Here are the details from a Winnipeg free press article.  Looks like the seatbelt got wrapped around her neck when she was pushed out of the car and dragged until the grisly end.
 
"Roberta McIvor had passed out in her 2005 Chevy Impala following a night of drinking in Sandy Bay.

The keys were still in the ignition.

The two teens — both drunk and possibly high on drugs — saw an opportunity for a "joyride" and jumped inside the vehicle, driving away with McIvor still out cold inside. After a few minutes they decided to lighten the load."