1) There is nothing illegal about a female employee being behind closed doors with male supervisors, managers or coworkers. Clearly, they may not sexually harass, etc., the woman, but this is not the case of going to a doctor's office, where a female has the right to have a female nurse or other office staff member present for examinations; in the employment context, there is no law against men and women being behind closed doors together.2) A supervisor may write up a staff member and terminate her regardless of her work history or how good an employee she is. If she had a written employment contract preventing this, that would be different--the employer (i.e. the supervisor) must honor the terms of the contract, and if there did not, the employee could sue for "breach of contract." However, without a contract, employment is employment at will, and a supervisor may discipline or terminate an employee at any time, for any reason.3) The owner could overrule the supervisor and take other action if he chose--for example, he could fire this supervisor and give you the job. But that is voluntary on the owner's part; if he lets the supervisor get away with this, there is nothing you can do.