Is it permissible to boycott the brother's wife who mistreats the questioner and her family, despises religious people, and rarely prays?

Firstly: Some scholars consider the one who abandons prayer to be a disbeliever, and this is the most preponderant opinion. Secondly: Your brother's wife's mockery, insults, and derision of the committed Muslims is a grave danger that could expel her from the faith, due to Allah's saying: (Say, "Is it Allah and His verses and His Messenger that you were mocking?" Make no excuse; you have disbelieved after your belief), and His saying: (Indeed, those who committed crimes used to laugh at those who believed... So today those who believed are laughing at the disbelievers). Insulting a Muslim is wickedness, and the one who insults may fall into apostasy if their insults are due to the Muslims' commitment. We advise offering her counsel and not sitting with her unless she repents. It is permissible to speak to her with greetings and inquire about her well-being without engaging in discussions that might lead to the unlawful, and to supplicate for her guidance.