Is it permissible to inform the husband of what his sister said about him, given that the wife knows that the sister curses her brother to their mother?

Slander (namīmah) is forbidden, and it is not permissible to convey speech between people with the intention of causing corruption, due to the Prophet's (peace and blessings of Allah be upon him) saying: "A slanderer will not enter Paradise." However, if refraining from informing the husband leads to a clear harm (mafsadah), then there is no objection to informing him. But it appears here that there is no harm in not informing him. It is more appropriate to advise the husband's sister to abandon backbiting (gheebah) and remind her of its prohibition.