The private pilot had completed a cross country flight and entered the traffic pattern to land. While on base leg the pilot applied carburetor heat, reduced power and extended landing flaps because she believed she was too high. Once on final approach, the pilot extended additional flaps. Upon extension of the flaps the pilot stated that the airplane began to decelerate and descend rapidly. The pilot stated the stall warning horn activated and the airplane rolled to the right during the deceleration and descent. The pilot applied power and forward elevator pressure on the control yoke. The engine did not respond with the application of throttle. During this process the pilot stated she lost sight of the airport. Shortly after this action the pilot performed a forced landing. An on scene investigation revealed that the right wing fuel tank contained approximately 1 gallon of fuel, and that the fuel selector was positioned on the right wing fuel tank. The left wing fuel tank was approximately 3/4 full.