So I feel like my situation may be fairly unique. My step-sister is absolutely INSANE. To try and make a long story short I will try and spare some of the more tedious details.
I have issues with my biological father, I have had issues with him my entire life. Lately it's been a little difficult, and his wife (my step-mother) and her daughter have been making comments that make me feel like I some kind of failure as a daughter, even though I have been trying the last 3 years to get closer to all of them. In fact, it's only gotten worse since I got engaged. Because of this, I decided that I did not want to go over to their house on Christmas Day. I didn't call him either, which in hindsite I should have, but I didn't feel like having an emotional battle on Christmas.
So here's where the issue comes in. My step-sister sent me some nasty messages on facebook. At first I just told her to please leave my relationship with my father between me and him, and to please stay out of it. She flipped out and much nastier, meaner messages followed in with she called me a variety of things like, "deadbeat daughter, poor excuse for a daughter, miserable human being" and she ended by threatening me not to mess with "her" family or she'll "beat some sense" into me.
Needless to say, she is no longer invited to the wedding. Even if she apoligized, I don't think I could accept it. I'm just worried this is going to cause problems with my dad and his involvement in the wedding, and our relationship is already so complicated. What should I do?