Having worked for Avis, Budget and Hertz in my 16 year rental car career, none of these companies would waive the OP's extra day fee. Rental car companies have to pay for the car regardless, just like you would on your own personal car if it is leased/financed. You don't call up the manufacturer and ask for a credit because you couldn't drive it for two days due to weather conditions.

While it would be nice (and charitable) for companies to waive extra day fees, it likely isn't going to happen.