Is it permissible to boycott the mother-in-law who speaks negatively and mockingly about the sick mother of the wife?

The mother-in-law should not be estranged; rather, she should be connected with and treated kindly, out of respect for the husband. It is possible to advise her and clarify the impermissibility of her actions. The husband should also advise her with wisdom and gentleness. Patience and contentment with Allah's decree are recommended.