She didn't really do anything at the cleansing. She sat there and acted as the conduit from which Rand was pulling Saidar. That is it. Also, she did not draw more Saidar than he did Saidin, because he was trying to cleanse the taint off of the *entire* male half of the source. Much like running one's through a machine to remove all of the toxic impurities that build up due to kidney failure, all of the blood is cleaned but not all of the blood is drained at once, as this would kill the person. He cycled the entire source through the Saidar "sheathe" but did not remove it all at once.