Toxic work environment

Hey everyone Im writing this on behalf of my wife. She started working at a McDonald's in California 07/2025 and its her first job. First couple of months she has had zero issues with her coworkers and management. She has been getting high praise from management and even the owner of the store for her work. Until month 5 where the main manager of the store (dont know the official title) has stated she wants to see my wife as a crew trainer. Which now they expect my wife to do that role without title change or pay. Which she has been doing but this isnt the main issue. Since being offered that role, the main managers sister who is also a manager there started to treat my wife in a bad way. She would scream at my wife that shes incompetent in front of crew members and customers on a regularly basis now. But in front of other managers or even the owner she praises her. What advice would you give my wife in how to handle the situation when she feels she cant to to management due to most of them being family members and even one of the HR workers is married to one of them?