Even if your manager did lie to her manager, it would not have made a difference. Employment is rarely guaranteed for a fixed period of time. It can end at any time for any lawful reason. Terminating an employee for failing a drug test is a lawful reason. Sorry, but the employer has the legal right to fire you under these facts.
They say you get what you pay for, and this response is free, so take it for what it is worth. This is my opinion based on very limited information. My opinion should not be taken as legal advice. For true advice, we would require a confidential consultation where I would ask you questions and get your complete story. This is a public forum, so remember, nothing here is confidential. Nor am I your attorney. I do not know who you are and you have not hired me to provide any legal service. To do so would require us to meet and sign written retainer agreement. My responses are intended for general information only.
Sorry, but what you report is not unlawful. Your employer is allowed to change its mind at any time about the issue, and the fact that one person or more at the employer would have hired you anyway does not mean the ultimate decision makes must live with that representation.
Good luck to you.
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It sounds to me like "the girl" who interviewed you does not have the final say as to who is hired. If they are drug testing new hires, that says to me that they actually do care what employees do on their own time. Especially if that employee comes to work with marijuana in his system.....and then works with families and children. Sounds to me like the company wants to protect itself against potential liability. I think you were rolling the dice by admitting to "the girl" that you smoke and also in taking the drug test when you knew it wouldn't come out clean.
It doesn't sound like you have a basis for a wrongful termination claim given that I'm guessing your being hired hinged upon you passing the drug test. Unless "the girl" put it in writing that she would hire you even if you didn't pass the drug test, I wouldn't count on her backing you up. I doubt she would want to admit to drug use herself as she might get fired as well.
***This response is provided solely for general information purposes and is not intended as legal advice. This response does not create an attorney-client relationship.