I certainly appreciate all the advice. Her Dad brings her to and from work, so that location is not a problem.
After much thought, this will be my "plan of attack"; My first step will be to ask the manager/owner to tell him to leave & never come back. If he does not agree, then I will ask him why he values one customer more than the safety of his employees. If he doesn't change his mind, I will ask her to quit. She values my opinion, so that shouldn't be a problem.
Then I will probably approach him & let him know that she is my niece, that I love her, & that I will protect her with my life. Then I will let him know that I know who he is, have his picture, & license #, and ask him to never show his face near her again.
I will do this in a polite but firm way, and I will be using a voice recorder the entire time, so that if he accuses me of threatening him, I will have evidence to the contrary.
I'd be more than happy to meet you at the joint and "help" you talk to him.