Histamine, and other amines are helpful, not dangerous.
Histamine can be extremely dangerous (even life-threatening) if you have MCAS or IgE mediated allergic reactions that can cause anaphylaxis. I have no idea if the original poster's partner has MCAS but if she does, it could be unsafe to eat high histamine foods.
I have encountered others who do not believe that MCAS is a real illness, so I am not going to spend a lot of time defending it, but histamine (and other amines) can be dangerous, or even life threatening, in someone who gets anaphylaxis. It would be negligent of me not to mention that in case it is relevant to the OP or anyone reading this thread in the future.