As a general matter, an employer may discriminate against employees, or treat one differently than another, for many reasons, including whom they like more or less. What they can't do is base this differential treatment on specifically protected categories; if they do, that would be illegal discrimination and could give rise to a cause of action or legal claim. The main types of illegal discrimination are based on race, sex, religion, age or 40, or disability; if your daughter believes she received worse treatment due to one of these factors, she should consult with an employment law attorney and/or contact her state's equal opportunity or civil rights agency.