Answer: Extinction
Explanation: Extinction literally means a state of non-existence of something due to gradual decline over time. Extinction also takes the same pattern in classical conditioning whereby a conditioned response gradually fades away or declines over time due to non-reinforcement of the conditioned behavior. In the scenario above, A behavior which Tyler used to perform everyday also triggers a similar response from her grandmother Rose, however, since Tyler has regressed in the reinforcement of her behavior( sending mails), the response from her mother also declines(checking mailbox), therefore if the non reinforcement continues on Tyler's path, Rose will completely stop checking her mail. Once this happens, Extinction has occurred.