Unless you have already fixed this problem, then feel free to ignore, and my memory is not so great --
I do believe that agreeing to extra security before the Crowns coronation is a big part in making sure your citizens and Yekbun dont die! In my own playthroughs-- I have prioritized my public over the nobles. I remember agreeing to extra security during the party(?) and my parade. I had kept the prisoner in the dungeons, and so, later-- Yekbun had only a simple cut on her arm!
Try agreeing to extra security in all ways and keeping the prisoner in the palace(if you wish) or sending them to marabad's prison!