My advice would be to just be patient as she gets through the first trimester. As a woman, it's really hard to explain how it feels to have mood swings...for me it's like this: I know how I'm acting, but it's almost like I can't control it and I feel like a different person during bad mood swings. I always regret it if I acted irrational for any reason.
So, just try to be there for her. If she wants space, give her space. If she wants you around, then make yourself available. If it is still really bad after awhile, look into family pregnancy counseling sessions that help couples deal with the pressures of impending parenthood. Might as well start now and practice your communication skills, because that is one of the most important things with co-parenting.
Good luck! As hard as it is on the moms...it's always just as hard on the dads.
~Jenn~ Mom to Ethan - my heart surgery survivor - born 6/29/09