I think you've kind of hit the nail on the head. Regardless of corner-cutting, poor working conditions, hurried schedule, overconfident actors, and so on, in the end it's the armorer's responsibility to ensure that the firearms and ammo are being handled and used safely. And she clearly failed in her duty.
Unless the defense can show someone switching out the bullets in the gun, then I don't see how she will be found not guilty.
I do have some sympathy for her because I think she was set up to fail, both by the production and by her dad. She clearly didn't have the experience, knowledge or training necessary to hold this position. At the very least she should have had a few previous stints as an assistant armorer (and I don't mean just shadowing her dad). But I don't think she ever realized her lack of competency. It's a true instance of the Dunning-Kruger effect.
