What is the ruling on dealing with a sister who is obscene in speech and respects no one, and is it permissible to boycott her for a period, hoping she might come to her senses?

A Muslim must be characterized by good manners in their words, actions, and dealings, especially with their parents and siblings, for Allah Almighty says: "and speak to people good words." Good character is the heaviest thing placed on the Scale, and its possessor reaches the rank of the fasting and praying person. The sister should respect her brothers and relatives, and the brothers should treat their sister with excellent manners. Regarding the sister's work in government departments, she must adhere to Islamic etiquettes and be cautious of khalwa (definition) (private seclusion with a non-mahram (definition) man) and khudu' bil-qawl (softening of speech) with men. As for shunning her when she commits something forbidden, it depends on what serves the best interest: if it leads to her rectification, then she should be shunned; otherwise, no.