I think you should go. She is the one being the drama queen. If you don't go then you guys just add fuel to the fire. Who cares? Its one day out of your life. Be polite and go to the wedding and that's it. Do not get in any fights on the wedding day. Just say congrats. Also, just an FYI going to the wedding does not mean that you have "forgiven" or even want to be friends with her. All it means is that you are being a mature adult and going for the sake of your husband's family. After the wedding you need not have any further contact with this person except like previous poster said at the rare big event.
She sounds like a crazy, overreacting b!tch, but she did apologize and tell you she wants you there. I think you should take the high ground and go, since it is a wedding. But after that, keep your distance, and if she lashes out at you in the future, tell her you're not going to let her treat you like that, and leave. She's not worth the drama. Any time you give her a reaction, you're feeding the drama monster!
Re: Sister-in-law from hell..
~Benjamin Franklin
DS dx with celiac disease 5/28/10
Also, just an FYI going to the wedding does not mean that you have "forgiven" or even want to be friends with her. All it means is that you are being a mature adult and going for the sake of your husband's family. After the wedding you need not have any further contact with this person except like previous poster said at the rare big event.