After creating the antidote, Jiang Chen decided to tackle Emperor Peerless' poison first because all clothing had to be removed for treatment. This was so one could make sure the poison was fully expelled. The Seven Emotions Poison was extremely lethal. Even a small speck left in the body was capable of growing into another lethal dose in merely a few days. Removing all traces of it from the body was of utmost importance.
Since the emperor was a man, Jiang Chen didn't feel the need to hold back. Considering the circumstances, he would've saved Madame Yun first, but his hands were tied because of the disrobing requirement. Thus, he decided to cleanse the emperor's poison first. The emperor could expel Madame Yun's poison after he was cured.
