Long story short, my fiance's sister is very selfish, immature, mean and condescending. Has been since we started dating, for no good reason. Now that we're engaged, her behavior is extra frustrating since my fiance wanted her to be happy for us but she continues to be extremely self-involved and childish. She also has been and continues to be very rude and dismissive to me. She clearly resents my presence at any family gathering, and when I dare to participate in the conversation she ignores me, avoids eye contact even when I'm addressing her directly, or just plain talks over me.
I've tried to deal with this by avoiding his family as much as possible, which is a shame because (after a few difficult years) I now get along with his parents and enjoy spending time with them. If she's there, though, I'm pretty much ignored and any conversation revolves around her. Parents are kind of clueless socially, plus she's mean in ways that aren't immediately noticeable. I bite my tongue a lot in an attempt to take the high road, which is thoroughly unsatisfying because she's one of those people that is too oblivious to notice that I could be nasty but am in fact trying to not sink to her level.
Am I obligated to include her in my WP, even though doing so would probably make everyone miserable? I don't want to offend her, but any attempts I've made to reach out to her in the past have fallen flat so I think in terms of an 'olive branch' this would be unsuccessful. I also don't want my fiance's parents to be offended on her behalf, as my relationship with them has always been rocky (they're a very difficult, antisocial family) and we're finally on good terms.
My fiance is extremely supportive of me not including her, and he is appalled by how nasty she's been. He's also upset that his only sibling can't be more excited for this huge event happening in his life.