I'm not going to my sister's wedding
Why are you not going to the wedding?
Because she's so sarcastic
Being sarcastic is not a good enough reason to not attend a special occasion. You both are siblings and should support each other despite not always getting along.
She called me an asshole.
I can see why you would be offended by that. Still, it seems like not attending her wedding is fairly extreme reaction that you are likely to come to regret. It's an act you can't take back, and one which is likely to escalate your conflict, or even break your relationship.