I'm sorry to say this sounds like something that could escalate. If I were the restaurant owner, I wouldn't think twice about calling the police. It is wonderful that you are concerned about your aunt. Maybe you can make a difference in her life and in the course of her illness. If she would like to be free of these delusions that is your starting place. Do you think she might agree to a trial period on medication, or would that merely be another "poison?" Sounds like it will be very difficult to reach her without arousing suspiciosns that you, too, are an agent of the CIA or in league with the gf of the restaurant owner, etc. And difficult also to get her to a psychiatrist. Your hands may be tied because she will refuse help.
You said she has job responsibilities and other responsibilities she seems to juggle okay. But still I would be they are all affected in some way by her obvious illness. And I am afraid I'm not helping much. If she could be convinced that her delusions are negatively affecting her whole life and the lives of others....? Perhaps there are some goals she is unable to reach because of this -- that might be a backdoor entrance for her to at least discuss what is going on? Probably not because delusions can be very powerful. And they do not often respond to reason.
Please continue to post here and let us know how things are going. I do feel deeply for you and your plight.
Carolyn