Hyperostosis frontalis interna is the thickening of the inner table of the frontal bone, which may be associated with hypertrichosis (hairiness) and obesity. It is commonly found in women approaching menopause.
Mega cisterna magna refers to an enlarged cisterna magna, a spinal fluid space in the back of the brain, just behind the cerebellum.
Since one defect is in the front of the head and the other in the back, it isn't likely that they could be confused. I'm so sorry to hear about your daughter. God bless.
As I noted, the hyperstosis frontalis interna is a prominence in the frontal bone of the head. It is seldom noticed in people under 40 and usually they are a decade older than that, so it is unlikely that it would have shown up on your daughter if she was only 30.....either in 2006 or this Spring.
Your daughter's mega cisterna magna would have been readily visible to even the most inept of coroners. While both problems can occur in the same individual, the lack of evidence of mega cisterna magna at autopsy casts doubt on the body being that of your daughter.