What should be done with an older sister who hurts everyone with her tongue and offers advice in a harsh manner, despite attempts to advise her to change her style?

A Muslim must be characterized by good morals in word and deed, especially with parents. The sister mentioned must fear Allah in her dealings with her mother and know that Allah has forbidden saying "uff" and every bad word towards them. Allah Almighty said: [So do not say to them, "uff," and do not repel them but speak to them a noble word. And lower to them the wing of humility out of mercy.] The questioner should advise her sister gently and kindly. If she does not respond, then patience and reciprocating ill-treatment with good deeds is best.