http://en.wikipedia.org/wiki/Slander
The common law origins of defamation lie in the torts of slander (harmful statement in a transitory form, especially speech) and libel[4][5] (harmful statement in a fixed medium, especially writing but also a picture, sign, or electronic broadcast), each of which gives a common law right of action.
"Defamation" is the general term used internationally, and is used in this article where it is not necessary to distinguish between "slander" and "libel". Libel and slander both require publication.[6] The fundamental distinction between libel and slander lies solely in the form in which the defamatory matter is published. If the offending material is published in some fleeting form, as by spoken words or sounds, sign language, gestures and the like, then this is slander. If it is published in more durable form, for example in written words, film, compact disc (CD), DVD, blogging and the like, then it is considered libel.
I am not an attourney but from what I understand, if it is true you cannot be punished for it legally, but you can always be blackballed within a company for it. Uness she is planning on leaving the company altogether she may want to take a different approach to the situation.
A better route to go may be to contact the BBB and make them aware of what is going on since if it is happening to her, it is probably also happening to others. If she feels this is race based, discrimination would be a better way to go. As far as bad mouthing her boss to a prospective employer, that is never a good idea in any situation.