Unless your discharge violated the terms of a union agreement or employment contract, you were an "at will" worker. This means that you could have been fired for any reason or no reason at all. Basically, your employer was free to set the conditions of our workplace much as it saw fit, absent some form of legally actionable discrimination (i.e. that based on a worker's race, religion, age, disability, etc.). And allowing the owner's niece to stay did not qualify as such discrimination.