To answer the question posed in the title of your question, the statute of limitations in the State of Washington for a defamation action is two years, a year shorter than for many other types of tort claims.
However, the tort of "malicious prosecution" may apply to facts like these, and the staute of limitations for that action is three years. To maintain an action for malicious prosecution, the plaintiff must allege and prove (1) that the prosecution claimed to have been malicious was instituted or continued by the defendant; (2) that there was want of probable cause for the institution or continuation of the prosecution; (3) that the proceedings were instituted or continued through malice; (4) that the proceedings terminated on the merits in favor of the plaintiff, or were abandoned; and (5) that the plaintiff suffered injury or damage as a result of the prosecution. Peasley v. Puget Sound Tug & Barge Co. 13 Wash.2d at 497.
As to whether "can my husband sue her" the question might be, "should he?" versus "can he." Does "she" have the financial resources to pay a judgment? She is described as a "girl" and there is a limit as to how much her parents can be forced to pay for intentional acts by her. Further, if there was no "probable cause" then the case should have been thrown out before it went to a jury. And the result of the criminal trial is not conclusive, it means the State did not prove its case beyond a reasonable doubt, it does not mean that the jury made any affirmative finding that the allegations were false.
More details would be neeeded to answer the question of whether such as case should be filed.
Bring your Washington defamation action within two years. Do not miss the deadline. You have rights but if you fail to act in time you may lose your rights.
Check with a WA lawyer in your locale to discuss more of the details.
Good luck to you.
NOTE: This observation is made available by the out-of-state lawyer for educational purposes only and is not like communication with a lawyer with whom you have an attorney client relationship along with all the privileges that relationship provides.
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