Is a mother sinful who knows that her daughter is lying and talking to a young man, but did not advise her, and is she culpable if she helped her conceal the matter from her father and brothers?

If a mother knows that her daughter is lying and speaking with a non-mahram young man, and she does not forbid her from evil and enjoin good upon her, then she is sinful, according to the Almighty's saying: "O you who have believed, protect yourselves and your families from a Fire whose fuel is people and stones." (Quran 66:6). Al-Tabari and Al-Sa'di mentioned that protecting one's family is by enjoining them to obey Allah and forbidding them from disobeying Him. If the mother advises her daughter, then the correct approach is to conceal the daughter's disobedience from her father and brothers, unless concealing it would lead to greater harm, such as if the daughter would not desist except by informing her father.