The laws about slander See R. Yona of Grondi [the book Gates of Repentance].
One issue that I wanted to bring here is that for some reason women nowadays think it is OK to falsely accuse men of sexual crimes. The reason for this is that even though people have heard of the prohibition of slander, they think that to bear false witness is OK. They are not aware that the main prohibition of slander is not just to say negative things about another person, but in particular to say things with intent to cause harm. [I can not say what repercussions there might be from this kind of sin,[probably hell], but I figure that women that lie about men think there will be no repercussions. At least we know that this sin is considered among the most severe. על שלש עבירות חייב אדם להיהרג ואל יעבור : עבודה זרה גילוי עריות שפיכות דמים ולשון הרע כנגד כולם The Gemara says On three sins one is obligated to rather be killed than to transgress. Theses are idolatry, murder, the sexual sins brought in Leviticus 18, however lashon hara /slander is equal to all three of them put together.]
And how does one go about repenting for such a sin? Sins that are between man and his fellow man do not get forgiven unless one goes to the person he or she has offended and asked forgiveness. For women that have slandered their ex-husbands or fathers in order to get revenge, it seems unlikely they will ask for forgiveness. So they might ask forgiveness in prayer, but that can not help until they ask from the one they slandered. And without that, the sin remains.
