Been there, done that.
While we don't live in a perfect system, immigration and courts included, the key to our happiness is within our grasp.
Many might disagree with me when I say that courts still favor women more than men, though that is now slowly changing into a balanced approach. I too have been a victim of false allegations, the same allegations if I had made against my ex (woman), I would have been laughed out of the court with my case.
But I was able to prove her false, her punishment for lying under penalty of purgery was, "Please be nice". Appauled though I was, I learned to make peace with this along with many other things, and moved on with life.
You can write a letter. Let's say she marries another person or gets citizenship and then sponsors another person, every time she applies for an immigration benefit, this letter will surface and questions may arise.
USCIS operates on proof of marriage, they don't care 1 bit about a good husband or wife, the pain you had to endure unless your case is VAWA.