What should I do *****family problem.?

When my sister separated from her husband she had no job and nowhere to live. I told her she could live with me. I even got her a job at my office filing. The next thing I know one of the girls in accounting is moving and my sister in line for a promotion. She would be filing as well as training for the next month, as the boss wanted to see how well she was suited for the job before offering it to her. For the next month, I tried to teach her as many things as possible at work and home. We always brought work home, but she was not picking it up fast enough, and I would just end up doing her work for her. Mistakes kept piling up, which affected my job. I honestly felt like she was trying to sabotage my job. Finally, I told her that if she did not become organized it was going cost me my job. Days later, my job is on the chopping block, (I was being laid off) and my sister is offered the promotion, which she accepted. She would be training for another 2 months. I was given the same amount of time to find another job.



That weekend my sister packed up and moved in with her daughter. Obviously, this destroyed our relationship. I could not stand having to work with her anymore. We did not talk. She was on her own. Then the girl in accounting decided to stay and my sister was back to filing. At the same time a position opened that was offered to me. Shortly after that, my sister gave notice and moved back with her husband. We have not spoken for over three years. She lives out of town so I just put her out of mind until now. My brothers son is getting married next month and all of our family will be there. All these years I hardly gave her a second thought, its been easy. However, negative feelings are cropping up again. I know having no contact was the right thing for me. Now I am not sure I even want to attend the wedding. I want nothing to do with her but I dont know how to handle it. I dont need my family giving me a hard time over it, either any suggestion?
Since this will be a family affair and most weddings have plenty of guests you can talk to I suggest you attend the wedding and avoid your sister. You don