I'm not sure what the difference is between the proof you'd find acceptable and a form letter to explain their findings. Your friend hasn't taken them to court.

ECJ judges seem to enjoy giving out EC.261 jackpots like candy, so your friend is welcome to try her luck. As WineCountryUA suggested, there are numerous European law firms who will accept any case that they think has merit in exchange for a percentage of the fees recovered. If the bird strike (or whatever damaged the plane) happened en route to Athens, I suspect even the ECJ would find that to be extraordinary circumstances. If the inspection happened in EWR, you might get one of the judges who believe that airlines should have an infinite supply of backup crews and planes parked at every outstation.

You're correct about a duty of care being due in any circumstance, but I can't imagine that winds up being more than the cost of one meal each.