Is it permissible to boycott a sister who is unjust, self-willed, and makes life difficult for those who disagree with her?

Your sister is considered a kin whom you are obligated to maintain ties with. It is not permissible to abandon or shun her unless she causes harm or corruption. The personal characteristics mentioned about her, such as being a domineering woman, do not justify shunning her. It is recommended to be gentle with her, respond to her ill-treatment with kindness, and supplicate for her guidance. Shunning was legislated for admonition, discipline, and reforming the shunned person due to major sins, not for personal characteristics. If shunning leads to the shunned person increasing in their sin, then it is not legislated. Therefore, shunning your sister is not advised; rather, you should show kindness to her, be gentle with her, and supplicate for her reform.