Good scenerio but you're still missing some info . What were fire's baseline vitals ? Thier baseline and any others would help establish a pattern . What was the MOI ? Was she restrained ? We know she has a life threatening head injury but could we be looking at major chest or abd injury also ? Don't get tunnel vision and miss something else that could be killing her too . Basal skull fx could be from a rear ender or a hit from flying debris in a head on .