The team discovers the diamonds on the bridal veil are fakes made of cubic zirconium when they fail to scratch glass. Cubic zirconium has a hardness of 8 on the Mohs scale, which is hard enough to scratch glass.
The bride was shot because she was between the gun and the intended target. The gun was located under a limousine (about 6 inches high) and was aimed at a homing device on the targets chair back (about 2 1/2 feet high). With both the gun and target so low, the bride should have been hit in the leg and not the head where she was hit and killed.
At the ceremony, the bride says, "I do", then she is shot. When they're investigating the crime scene afterward, the detective says that she took a bullet before she could say "I do".