re: Any tips on how to teach a dog to stop on whistle.

First, is the dog collar conditioned? If not, then she has no idea why you are shocking her. Stimulation should only be used when the dog knows right from wrong. From your orginal post I don't believe the dog knows right from wrong. Her training tells her there is a dummy out there is should retrive it. Like another poster said get a check cord blow the whistle make her stop and then proceed. Probably after the 3rd or 4th time her butt will drag the ground like a wormy dog when you give the command on a retrive. Best of luck to you!!!