Answer:
stimulus discrimination
Step-by-step explanation:
Mrs. Ridcully probably attempted that her conditioning (her own specific whistle) would eventually be generalized and other similar stimulus (dog owner's whistle) would generate the same conditioned response, but she failed. Instead, the dog discriminates Mrs. Ridcully's whistle from other people's whistle and will only respond to her.
Stimulus discrimination happens when the subject is able to differentiate between different stimuli, and will only respond to an specific stimulus.