She is liable, there is no maybe.
She is responsible for approving the safety of every weapon on set, thats the definition of her job. Shes the armorer. Thats what they are hired to do. There is no maybe.
Alec is definitely liable as a producer who jointly ran the company that hired her.
You are right, and I agree with what you say. However there is one mitigating circumstance, and this falls back onto Baldwin in his Producer role, she was doing double duty on the set as both Head Armorer and as Property Master, and that is why she wasn't personally on the set that day with the firearms. She was off on another set dressing it with props.