Do I have any legal recourse for being fired after the person I replaced asked for their job back?
I was offered and accepted a job recently. I was in the training period and everything was going well. I was called into the supervisor's office and informed that I was being "let go" because the person I replaced had come back and asked for their job back and they were going to give it to her. Is this legal?
I'm afraid that you have no apparent recourse here since there was no wrongful termination. The reason is that most employment relationships are what is known as "at will". Basically, this means that you can choose to work for an employer or not and an employer can hire or fire you for any reason or no reason. While seemingly unfair it's the law.
The exceptions this would be if this action was not allowed by virtue of an employment contract, union agreement, or official company policy statement. Also, discrimination must not have played a role in your termination. Absent any of these circumstance your firing did not violate the law.