Mr. Mime started disobeying Stella when she trained it quite roughly. Attempting it to be jealous, she went to capture a Mr. Mime and failed. Brock had Ash disguised as a Mr. Mime to do the same effect, but didn't work out as planned.
When it was chased by Team Rocket, Delia's Mimey appeared and used Barrier. Stella's Mr. Mime used Barrier as well, encasing Team Rocket until they blasted off. Because of this experience, Stella's Mr. Mime started obeying her.