Legal Question in Entertainment Law in California

I don't know what a model manager is but I don't think there is any law about who can represent a models. Employment status depends on the various factors but I believe that models on a short stint are independent contractors.

I worked as an extra when I was in college and they sent me a 1099. I imagine models would be very similar.

The difference between agents and managers is that, legally, an agent is an employer (finding and negotiating work for the model) and a manager is an employee. The manager works for the model as an advisor, but legally is not permitted to negotiate or find employment for the model. Again, legally, a model is an employee (even on a short-term basis) of the photographer or studio that hired her/him, just as all crew and cast on a film are employees of the producer, and should receive paychecks with appropriate deductions. All too often, though, employers incorrectly treat these workers as independent contractors--usually to avoid paying employment taxes, unemployment insurance, and other worker benefits. Such employers expose themselves to heavy fines and penalties if someone reports them.