Wait until she turns around
So it appears as though one of the bridesmaids has caught the bouquet and everyone was in on it so that her boyfriend could propose. One of two things is happening here. The first is that she’s overcome with emotions because she’s realized what’s happening.
The other is that she hasn’t realized her boyfriend is right behind her and she’s about to get the shock of a lifetime when she turns around and sees him prepared to propose. Either way, the photographer captured an incredible moment.