The SIU investigates fraud. Did you take the $4,000? If you did, (plus) get paid the $5,664 from her insurance, then that is fraud.
Now lets say, that she told her insurance after you filed a claim, that she paid you $4,000 and you did (not) take or receive the money, then they may need to confirm in fact that she did not pay you.
Losing her license since age 80, could depend in the state where you live if you have an accident. I asked my state DMV if there was an age limit where you are not allowed to renew and was told no.