I am seeking a lawyer to assist in a civil / defmation / slander lawsuit against a large corporation. I need to know if I have a case?

You would have a case if the person making the false statement either knew it was false when she made it, was reckless in saying it without caring whether it was true, or was negligent in not determining whether it was true before she said it.  In other words, even though this person made a false statement, it is not a slam dunk that you would win, and your actual damages, since your reputation was rescued and you still have your job, are minimal.  This type of case would probably be considered what is known as defamation per se, meaning that you would not have to prove actual damages to be awarded damages by a jury, but given that the person has apologized to you, my guess is that a jury would not be likely to award you a great deal.  Moreover, if you wanted to sue, you would have to make yourself available for scheduled depositions and court appearances, which could be difficult if you travel a lot on your job.  Rather than going through the hassle and expense of a lawsuit, you might be better off just asking for the manager to pay you for what you lost by  having to stop the trip and come back.  She might be willing to reimburse you voluntarily.