Assuming she actually dropped it off. Several posters have made the point she could have wrecked it or kept it and just returned the keys.
true, but it’d be unheard of for a car lot not to have some security... if even just a camera... to secure a lot with 10+ cars worth $25k+ each
If they don’t have cameras and write contracts that require the car be returned on days they choose to have no one from their company present, it is entirely by their choice and entirely their fault.
I’d find it amazing if they don’t have cameras on their lot. They likely have a record of both the car being dropped off and the keys being inserted in the drop box as per their instructions. Otherwise they’d be saying the car was never returned - which they aren’t.