Hello again, ron:
What has been said here, is true. If your wife was a nogoodnik, then you don't have a legal claim. However, you state quite clearly that your wife was badmouthed to keep her from working for a competitor.
IF that's the reason (and I believe you), then she DOES have a case. If you sued for slander, then the specific words they used will come into play. You're going to have find out exactly what those words were (not an easy task), then you'll have to prove the words weren't true (an even harder task).
That's why slander isn't it. Defamation of character might be it (your lawyer will give it a name). But, it doesn't matter what you call the tort. What matters is that you kick that liars butt.