Thank you for trusting your question to JA today. I am a licensed attorney with over a decade of law practice and over 20 years of experience in the legal field. I’m happy to be of assistance.
Unfortunately, nepotism and even favoritism is not illegal in employment law. Some governments have recognized the damage it can do, and don't allow it for state jobs. Many employers recognize it and make it against their policy. But it is not illegal.
Unless you have a contract of employment that specifically guarantees you a certain job, certain tasks and a certain rate, your employment terms are "at will" and can be altered at any time, so the changes to your situation (though unfair) are also not illegal.
The one thing that you have mentioned with any sort of potential as a legal violation is the statement that this other employee lied about you. You could sue that employee for defamation of character, particularly if you lose the job based on her lies. However, from an employment law perspective, you have not raised any issues of illegality.
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