Cantonese and mandarin are totally different. My parents and elders speak their village dialect which closely resembles Cantonese. As an American born, I can understand much more than I can speak. However, I cannot understand any Mandarin except for the few phrases I learned in class.
Anyway, my point is that they are not easily interchangeable. To become fluent, Michelle would really have to immerse herself in it. I'm sure working with other skaters from China (ie. Lulu,etc) on COI has given her the opportunity to pick up non-textbook phrases, but I imiagine that Michelle still needs an interpreter to have an in depth conversation with the President of china.