The armorer is denying responsibility. The only way I can see she would even have a chance of that would be if due to covid restrictions she was kept away from the set, and was directed to safe the firearms and leave them outside where they were shooting the scene. They may have been there for hours. Rather than guard them, she would have gone off, leaving the guns unattended.
Then they may have been tampered with (deliberately,) or misused (inadvertently creating a dangerous situation). I can't see what other defense she could come up with.
I believe she was the one who took the fired shell out of the gun immediately after the incident, so she may have thought that she had previously checked it, and wondered how it got there.
Next, the sheriff claims: "Mendoza said 500 rounds were located on set, which were a mix of blank ammunition, dummy rounds and, possibly, live rounds."
That description is important. They knew there were dummy rounds on the set - but they will not now say that there were live rounds - only "possibly" live rounds.
Which means even they couldn't be sure whether the rounds there were live or dummy rounds. Secondly, they are not saying for sure that live rounds were seized, even though earlier reports have insisted many live rounds were seized.
And, I guess we still have the possibility of a squib round. You can’t “look down the barrel” of that gun completely. The only way that would be identified by putting a rod down the barrel. Had the armorer done correct procedures on the guns, as she claimed, she would have done that. After the Lee episode, I’m sure that is drilled into the head of anyone handling firearms on set.
A dummy round cannot be fired. It is inert. A blank can be fired, but they are not dangerous unless safety protocols are ignored. The Reuters headline makes it clear that the round was live.