1) If you do not have an employment contract, you are an employee at will, and may be disciplined (up to and including termination) for any reason, at any time--including for a non-work-related coonflict with another employee. Employers also do not have to verify the truth of any reasons or grounds for taking action.2) If the co-worker/roommate knowingly or intentionally made untrue factual statements about you which damage your reputation--such as claiming that you stole, when you did not--then you may be able to sue her for defamation. Only untrue negative facts are potentially defamation: true facts or opinions, no matter how negative, do not give rise to a cause of action. If you think you may have been defamed, consult with a personal injury attorney to explore your options.