Where's Ms Bee when you need her?
Clearly the Reg is lacking in knowledge of female clothing.
Underwire is not "wire lining". Not even in Old East German bras.
As Stork says, a rebounding bullet (wtf is a rebounding bullet? it's a bullet - not a basket ball) will be unstable and would have shed most of its energy. It certainly would not be likely to kill her.
About the minimum you'd need to kill a person with a direct hit to the chest would be a .22 and that would cut straight through an underwire. I have shot .22s through a car door [details redacted] and that's way stronger than any underwire.