I think you are deeply confused about various scenarios where duty of confidentiality is involved. She is not your therapist or doctor or nurse; she is not your financial advisor or your banker; she is not your landlady who obtained your credit report for the purposes of deciding if you are a trustworthy tenant and who has a federally mandated duty to keep the information she received via running that credit check on you secret from anyone but you. She is not your trustee. She does not owe you a duty of confidentiality.

Yes, if you have an ongoing repeated relationship with a cleaner, it is reasonable to expect that she would keep secrets and not tell others about whatever she finds in your house: marijuana vaping pens, condom wrappers, or whatever. This lady does not have an ongoing relationship of implicit trust with you. Plus, I agree with Divine that safety concerns trump here. It is not that she inadvertently saw a sex toy in your bedroom which is innocent but might embarrass you: she saw a gun. A GUN!!!

The referring lady needs to know that your house is not safe so that she would not send other unsuspecting cleaning ladies to you.

You are expecting too much from this cleaning lady whom you have not even paid. You have very high standards for others.

Regarding that it was not your fault that the gun was there but your husband's fault: it does not matter. I tried to explain it to you by analogizing to workplace safety laws which are strict liability laws, i.e. whether you placed the gun there, whether he did, whether you knew of the gun or you did not is completely irrelevant. You as the employer failed to provide safe working conditions and that is all. It is your responsibility. You owe a duty to this cleaning lady. She does not owe you any duty. She has a right to blame you. You can then turn around and blame your husband and you will be well within your right to do so, as ultimately it is his fault, but vis-a-vis this lady, you are responsible.