When Carly is shown back home after the first interlink with her Mother she is in the kitchen with her back to the kitchen bench. You then hear the kettle whistling to tell you it's at its boil. Only when Carly turns round you see that the kettle is electric. To have a whistling kettle it would have to be on a gas stove.
Edit:
There are electric kettles that do whistle. You've just never seen one until now.
Furthermore; It does not matter if a kettle is on a gas or electric stove. The water boiling is what produces the whistle. Not what causes the water to boil.