I believe this could have all been resolved quite easily by having a female guard pat down and check the underwire bra, determining it is indeed just that. I was checked in this way at an airport - the guard was discreet and apologetic - no harm done - and it was determined I wasn’t packing heat or a bomb. lol.
Well did it ever occur to you they might not have had one or how about this, perhaps the one they do have was eating, on break or indisposed when this female passed through? The fact is they did give her options and she had a choice although I think the one she took was wrong that is her fault not the guards.
The last time I went to a federal court house (jury duty thankfully) the rule was unless you had proof of internal metal there would be NO beeping going through the metal detector. Anything that might beep needed to go through the x-ray machine, and they had a pretty serious list of suggested items including belts and shoe inserts (being a guy I didn’t wasn’t looking for words like bra but I wouldn’t be surprised). They didn’t want to do any pat downs or any of that, put all your metal in the tray for the x-ray and step through and pray for no noise. And this was before 9-11 and the world getting afraid of terrorists, federal courts apparently are just very intense.