More accurately, she won't join the mansion until chapter 5, but there is nothing stopping Emma from being interacted with in her own unique way. Canon-wise, after the events of the Phoenix saga, things become very cloak-and-dagger between the Hellfire Club and the X-Men, so Null spending time with Emma as part of a spy mission from Xavier isn't out of the question.
Emma would know this and encourage it because seducing Null to her side as her White Knight gives her an edge over the other Hellfire Club members, especially once Selene joins. Seriously, that's probably what interests Emma in Null in the first place, as power nullifiers are rare as hell, especially ones that are as physically capable as Null (well, ones that are actually sane).