I found the video back that shows the case. Putting the rest in spoilers.
Without Tav there can obviously be no conversation before SH takes action, so like in your case she confronts Dame A. directly. Now there are still 2 options shown in the vid. If SH carries Shar's spear, she execute Dame A. But you have the option to make her throw away her spear before confronting Dame A. And then she is spared. If you have a save to reproduce your case you might try to see if you can throw the spear away also.
