>>96409152
I'm jumping in to this shit because I want this discussion to end. So, the lore suggests that sisters can technically fall to chaos. However, it is so unlikely and exceedingly improbable that you could count the amount of 'fallen' sisters on a hand. Moreover, even if one were to truly fall, they'd be killed rather quickly since they live a monastic life with other sisters and it's not like that kind of thing could be kept long from them. Thus, it has very little impact on the setting in any conceivable way.
In other words, you are not getting chaos sister units. You're as likely to get those giant whale things the Tau allegedly ride as models. Shut your traps.