Regardless of what is or isn't know about the mechanics/forces of an injury, it is the symptoms that should be treated. Amnesia or confusion are just a small part of the symptoms looked at. It might be more valuable for an observer to comment about the changes seen in the injured, such as, she is never this confused.... etc.

I doubt the doctors will change their diagnosis much upon hearing the rest of the story. They can only treat what they can see and diagnose.

Why didn't you file assault charges against your sister ?