Is there a sin upon one who tells her children about the injustice of their grandmother, while urging them to respect her?

A wife's patience with her husband's mother is better for her in the sight of Allah, for it is among the resolute matters that Allah loves. It preserves affection between the spouses and safeguards the children's feelings. However, if the wife openly declares the injustice she suffered from her husband's mother, she is not sinful, because Allah does not love the open proclamation of evil speech, except by one who has been wronged. It is permissible for the wronged person to speak about the wrongdoer's injustice and to supplicate against them.