I don't think she faked it as she had participated in a few tournaments previously this months. Off the top of my head, I know that she played two long games, NOT sets, against Zhang Ning in the MVP Cup just last week and right before that she played in the Chinese Taipei Open where the two met again. According to Gill Clark (???), the scores were pretty close (21-19 & 30-28 or something like that) indicating that it was long and tough battle for both.
She might have played in the Macau Open & Malaysian Open this year as well but I am not sure. Anyway, those games finally took its toll on her. Even Zhang Ning withdrew from this tournament so I have to applaud Yao Jie for staying in the tournament till now.