She remains an antagonist for nearly a decade before mellowing out in the 90s.
Several events are directly caused by her being an antagonist, so her joining outright before she mellows out is unlikely.
Note, there is nothing stopping Null from seducing her to spy on the Hellfire club, as he is the only one immune to her powers outright, or Emma tries to seduce him to do the same to the X-Men. It would work out even with no romance, as you can do back-and-forths while eating fancy dinners or meeting in social encounters.
It would be a vastly different romance and character interaction compared to every other character, but it would be something fitting to the character, in my opinion. It's also not without precedent in the comic, considering the number of times the X-Men just walked up to the Hellfire club. Heck, Magneto even joins the Hellfire club when he was still the leader of the New Mutants.
Potentially, but in the arcs the game will be covering, she is outright retired and doesn't rejoin the plot in any significant capacity till Mr. Sinister has Malice possess her and then she joins X-factor when she is freed.
If it's going to be comic-accurate, then Null won't even interact with her that much beyond the times she is briefly mind-controlled and when she shows up for Scott's wedding. Now, the devs who put far more thought into this than I did might know a better time she can join, but the best time I can think of is chapter 5 where she joins the X-Men instead of X-factor. Heck she might not even be joining considering the sheer number of other potential girls joining in the same time frame.
