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I am sorry to hear of this very difficult situation. I suggest that you consult with a civil litigation lawyer. This issue really is not for a family lawyer.
If your former spouse is telling lies about your current spouse this is defamation and she can be sued for damages to your spouse's reputation. But, the first step that has to be taken before a lawsuit is initiated is you must have a lawyer send her a letter demanding that she cease and desist, provide your spouse with a written retraction and apology, and threaten a lawsuit.
If she refuses then your spouse can sue her and seek an order enjoining her from defaming your spouse further and for damages.
Does that help as a starting point?