You were the employer. She was the employee. Have you ever, as an employee, seen those posters in break rooms about OSHA and CalOSHA? Employee safety is the law. It is just that the law does not yet reach the unregulated scenario of domestic services. But workers' rights become stronger and stronger as years go by and what is the law now would have been unheard of just a few decades ago. I can easily imagine how in 10-20 years a person who has gone through the shock you put her through can have a claim against you for infliction of emotional distress. Laws about safety are strict liability law, in other words your state of mind, the fact that you yourself were surprised by finding a gun, is irrelevant. You, as the employer, failed to provide a safe working environment for this woman. That you apologized is not enough, in my opinion. She was scared and she (I agree with the above) simply invented the excuse of a house too messy because she was afraid to tell the truth, that she did not want to stay a minute in the house with an unlocked gun. That is probably she involved that other client: she was afraid to tell you directly. She wasted time on top of being scared: she could have cleaned another house and made money. If I were you, I would text her again, offering not only another apology but also payment for 2 hours (usually all service providers charge a two hour minimum).

I honestly find it shocking that you do not see the situation as that of you failing the duty to provide a safe working environment, and finding excuses such that many people own guns.

I have never cleaned houses but I can put myself in her shoes and tell you for sure that I would not have stayed a minute in your house. And I am not gun-phobic and have never lost anyone to gun violence.

I also find it disturbingly one-sided that when you regard yourself as a victim, you find fault with other people's relatively minor infractions, such as the Big Mama comment not directed individually at you, but when you (unintentionally, but still) inflict serious distress on an innocent victim, you insist on being well within your right to do so.

Similarly, you wrote: "She arrived 15 minutes late with no text. ". So you see her small failing as the employee, but you do not see your big failing as the employer.

The Biblical saying "Why do you look at the speck of sawdust in your brother's eye and pay no attention to the plank in your own eye?" comes to mind.