If my sister weren't a raving lunatic I would simply opt not to go...but here's the thing: if I don't go she will become VERY belligerent and vengeful. She has been like this since she was a teenager. She's been known to tell lies about people when it suits her. Years ago she was caught sneaking out of the house. She threw me under the bus, then; telling our folks that I did the same thing as a teen (I didn't, not even once. She, on the other hand, hung out with huffers and got nailed for underage drinking at least twice, then flunked out of community college...got knocked-up when she was 20, then again <2 years later). I shudder to think what she would do if I decided not to attend her wedding. The sad thing is that of everyone in her immediate family and friends, I am the one most financially able to attend and stand up. She thrives on drama and would make a ton of it if I bailed, I'm afraid.