What can be done when someone is hired as an independent contractor, but does not receive compensation for their work for several months?

I’m asking this on behalf of a friend. This is her own explanation of the circumstances, taken from an email:

“I was hired to work 3 scheduled hours a day M-F for 1,000 USD per month

They said that because we are contractors that it accounted for a delay in the set up of the payment process. Other people that have this same position had waited a couple of months in the past to begin receiving payment. Once they had they received what they were owed in one sum they then had no problem receiving the monthly pay.

Now since I have been brought on, the difference is the other contractors that I mentioned are independent and at this time I am being told I will get paid through a temp agency and become an contract employee through them. I am worried about that agency providing the total I am due when they will have discretion over aspects of my work and rate. Basically I am worried that if I encounter any trouble with what I am owed from what I have already worked it will be in the hands of the temp agency. I have already had a bad experience with the temp agency as I had previously submitted documents to them twice and nothing came of it. At the time I was under the impression it was a payroll service.”

-Now this agency is requesting the same documents she sent before, plus several others, before they will agree to pay her.

-She has been working for this company, which is a huge, well known, international gaming company, for 4 months… without any compensation.

-She did not sign any contracts with this company, however she has emails and public conversations where it is stated that she was hired, and had a regular work schedule.

What should she do? Does she have any way to ensure that she receives the original pay agreement of $1,000 per month? Should she continue working for this company, and how can she be absolutely certain that she receives the compensation owed to her?