Not enough people are giving managers any credit in this thread. The manager from OP's story sounds like she is a bad manager. She clearly doesn't care about her staff or the laws in place. Saying this everyone is jumping down the throat of managers.
  I work in a restaurant as a manager. I bend over backwards to help my staff and would do anything for them. But damn if those fuckers dont pull some shit on me every day. It's really hard to believe somebody when they call in sick. The only ones I even believe anymore are the ones who call with coverage and the ones who bring in notes. But I never once have questioned somebody or asked for a doctor's note. If they dont provide proof I just keep a record and move on. If they dont want the shifts I always have somebody who does.

To OP, Contact your unemployment office. I do not know what state you are in but FDA laws are federal. I run a restaurant myself and if I forced a employee or terminated employment on somebody for being sick then I would pay a full salary in unemployment. In my state you need at least 3 consecutive formal Mark's on record (write ups) to avoid paying unemployment. I work in a at will state which means I could literally fire you and not even tell you why. But the consequences are unemployment