Crash investigators do this for a living?

Sorry to hear this, I hope she recovers well

Not to play devil's advocate here, but if her insurance is sufficient, I wouldn't even bother suing (purely personal prefference)
Now, given the severity of the injuries, and cost of care, the air lift alone could eat up an underinsured drivers coverage, and then you have no choice but to sue, but if you could avoid the headache, I would