What would be your "comfort zone"? Where would you prefer to be, in the wedding party or more comfortable sitting in one of the front rows?
I recall the first wedding I was in. The groom was one of my best friends and wanted me to be his best man. However, his bride had invited every girlfriend she knew that since they weren't in other weddings they could be in hers. Ten bridesmaids. So many that it was decided we all would be arranged and paired by height. Needless to say, I was the tallest and so rather than being the best man I was the 10th man.
I'm not saying you should or shouldn't be in the wedding. I do say there are many factors involved and some could rise up out of left field.
There is something to consider about BPD traits. Often some distance and less frequency of interaction reduces the level of discord. If you've been on the periphery of your sister's life recently, you might ponder whether the relationship and reduced conflict might be due to the less interaction. Or whether instead it may be that over the years and with increased maturity she may be becoming a less problematic person. Something to ponder.


