To be accurate, a person can experience a head injury which results in a slow bleed that eventually kills the person but in the meantime, the person seems fine.
However, if the ME has any competence, something like that would be the first thing he or she looked for.
The fact that the ME says the girl’s death was not as a result of the head trauma to me indicates that, in this particular case, the death was not the result of the fight.
To be accurate, a person can experience a head injury which results in a slow bleed that eventually kills the person but in the meantime, the person seems fine.
I had a friend who fell and hit his head while walking his dog.
He got back to his front porch, and was dead within minutes.