Michelle's last 'competition' was Dec 2005 in the vote-in compeititon. She was in the top2 even though she had just resumed training and was clearly not in shape.
Also, according to Wikipedia, she last skated for COI in 2006 and then had surgery.
I think she has gotten on the ice when she went to China as a public diplomacy envoy, but it may have just been skating around with the kids - not a performance.