I would think that if it was the heater core you would be smelling anti freeze. Can't wait to find out how you made out at the dealer.
That's why I do not think it is the heater core. I'm hoping that the water came from a door seal. It would be easy enough to test for.That much anti freeze would leave a film on the inside of the windows. You didn't mention if you had any rain lately to allow for water to leak in somewhere. I believe that the A/C is leaking condensation into the car instead of flowing it to the outside of the vehicle.