The only thing that counts in TV competitions like "let's dance" is personal charisma. It's not just the charisma of the famous pupil, but also the charisma of the teacher. Some of the participants, even the professional dancers, seem to think the result has to do with dancing technique...! The charisma would also explain why there is often the same professional dancers in the semifinal and the final every year. It's not just that they make good choreography and can teach dancing efficiently, the charisma makes the difference!
Tonight it was interesting to note (according to my conspirator theory) how the show were trying their best to make the actress look bad. They were mentioning famous relatives and insulted her mother and so forth. Do you understand why they would do that? Maybe she doesn't have rich sponsors as the singers must have?! Well, I'm glad that strategy wasn't successful!