"...he (Qi Xia) was surprised that she could change her mind in such a short time." Eh, "short time" is a relative to which starting point you're using. If it's when she saw the BSP reaction to Xiu's identity, it's indeed a "short time". But, if we're talking about when she heard about the plan of Devil's God in three years, it's a "long time." Because when the ones who came to attack her and her people and the one who instructed/allowed/acquiesced in the attacks were just a few members of BSP; Even when she knew Su He's experience in BSP and he's not the only victim; Even when she killed the timid teenager Ah-Qi; even before she saw their reaction to Xiu's identity... She still didn't care if human race only have a handful second stage professionals on the upcoming war against Devil's God. She still didn't care about those innocent cultivators who's deceived and/or coerced by the higher echelons of BSP. She just wanted to kill all of them.