Is the questioner considered a partner in the sin of her friend who got married without her family's knowledge and then aborted her pregnancy, and is she sinful for revealing her friend's secret to her husband, and how can she expiate her sin?

If the marriage proposal of the girl is accepted by the husband in the presence of two witnesses, then the contract is valid. If it is without two witnesses, there is a difference of opinion, and the majority holds that it is invalid. Abortion is not permissible except if there is a danger to the mother's life. The predominant view is that it is forbidden before forty days unless there is a valid excuse. You do not share in the woman's sin unless you guide her to it or agree with her. However, it is not permissible to issue a fatwa (definition) (religious edict) without knowledge. Informing your husband about the matter is not permissible except for consultation and seeking advice. Repentance involves abandoning the sin, regretting it, and resolving not to return to it. If the sin involves the rights of a human being, then it is a condition to restore the right or seek their forgiveness, based on the Prophet's (peace be upon him) saying: "Whoever has wronged his brother concerning his honor or anything else, let him seek his forgiveness today before there will be no dinar or dirham..."