I asked some of the questions raised here to people involved with the production when it played at Symphony Hall. I especially asked why the first act didn't end with Sarah's death. It was re-done to accommodate an intermission similar to the way it's done at a regular Pops concert and the whole thing reduced to fit into a Pops concert time frame. Not ideal but that's how it was done.
It was clearer in Symphony Hall that it was a gun shot.
I was able to hear the Tanglewood concert on WCRB....Elizabeth Stanley sounded wonderful.