I wouldn't go. Perhaps you could visit your sister earlier in the day before everyone arrives. About 5-6 weeks into my sobriety my daughter had a housewarming party, I really was not comfortable going but felt I had to make an appearance. I told my daughter ahead of time that I would only stay for a short time. I arrived about 30 minutes before the party started because I had not seen my daughters new home and visited with her and her family, and I left about 15 minutes after other guests started to arrive; it was very scary for me and I knew that most all the people coming had seen me at one time or another drunk out of my mind so I also felt a lot shame and embarrassment.