Sibling relationships can be so complicated. I feel for everyone here who has a strained relationship w/ a sib or who has to "watch" their AC fighting with or distancing each other. Sometimes, though, IMO, if family members have a tense relationship, they are better off w/ some "space" from each other, as sad as it may be.
Juel, I'm glad you decided to accept your friend's invitation. Chances are, your sister won't show, and if she does, she'll be nervous, too. I think you've been given very good advice as to how to handle things if she "kicks off." Hope you let us know how it goes.
IME, some people get really zealous about their political beliefs. So it's possible your sister really can't/won't tolerate anyone who doesn't share hers. But I agree her anger could also reflect other underlying issues, especially given your brothers' perceptions. Either way, I don't think you can fix it. She needs to sort out her own feelings or keep her distance.