A 2 point strut brace, front or rear, isn't going to do SQUAT to stop the motion that would cause the window frame to go far enough out of square to break a window. The way to prevent this is to put an x-brace over the rear seat opening like the Boss 302 LS has or a cage. A two point brace out back is only going to force the shock towers to move in the same direction and I'll be perfectly honest, there isn't enough force there when the springs are still located in the stock location to justify the brace. They provide no rigidity in the direction these forces were producing (torsion about the horizontal longitudinal axis when looking in front/rear view).
I'm willing to bet something else happened here though. Bad wheel hop is a good guess.
