The Armorer has one job. Keep track of the weapons at all times. She was not doing her job.
Yes, she has fault in this incident. She is not the only person at fault.
"Troubles never singly come, but march in three abreast" (Proverbial)
The armorer had more than one job. She was also a wardrobe assistant or something. That was part of the problem. They didn’t want to waste money on a full-time or qualified armorer.