Crash investigators do this for a living?

I have some experience with accident investigators. Odd to me that there was an investigator on scene or was he there later the next day? Their determination depends on who hires them. Yeh, I know, you think they should be impartial and only look at the facts. Nope. Not how it works. Who hired the investigator to look at the scene? The County?
As for speedometers indicating the speed at the accident, yes that does happen. Far as I know it is not admissible evidence in court. Aviation investigators often use instrument needle slap but, they are only investigating and not accruing evidence for a court case.
I'm not sure but, if the police report says "no seat belt worn" and it's required by law, her insurance may not pay or they'll at least try not to.
Who arrived at the scene first? police, EMS, another motorist. Like others said, get their statement.
Unmarked road with out any warning signs, e.g. "Unmarked Pavement Ahead" is a cause for blaming the county.