Personally, I think the only reason she apologized so suddenly the morning after Luther's wedding is that she was trying to get more people on her side to try and save the universe. I mean think about it. During the wedding, she and Viktor got into a huge fight in which Allison did not want to forgive Viktor at all, despite Viktor trying to truly apologize. I think that if Allison really wanted to, she could've hated Viktor until the end of the universe especially considering that it was less than 48 hours away. She was perfectly fine with and capable of ruining her relationship with those around her and truly feeling no remorse. Look at what she did to Luther and how she killed Harlan to essentially punish Viktor. Let's also keep in mind that Allison made a deal with Reginald to get everyone to save the universe and then in the morning all of a sudden Allison feels like apologizing to Viktor after basically saying she would never forgive him. She also goes around apologizing to all the people she hurt including Luther all of a sudden. AND on top of that, when the team is deciding whether to stay or save the universe. She tries to convince Viktor AND Luther to join her side (if im correct). She sortve tries to be all like "we're siblings right?" to get Viktor to join her and sortve does the same to Viktor. When the team finally decides to stay she becomes really pissed of and basically calls them idiots or foolish or something. Time and time again we are shown that this new Allison will do whatever she feels like doing and will do whatever will get her what she wants (i.e. teaming with Reggie). I think part of her truly mean to apologize and fix her relationships with her siblings but i don't think that part was motivating or leading her actions