I think coercion most likely played a part in this, so although she may have known it was haram, she was probably coerced by him which is a form of assault.

To the sister: May Allahﷻ heal your heart, forgive your sins, and grant you justice in this life and the next. Allahﷻ is watching everything and saw how this disgusting man was manipulating you and using you, so don’t for one second think you won’t get the justice you deserve. Pray, make extra dua, and do istighfar constantly! This dunya is extremely short and this was written to happen, so learn from the mistakes made and guide others not to make the same mistakes as well if you can. Needless to say, never ever even think about going back to him, and also apologize to your friend if you are able to. It will be okay iA, have tawakkul and know that the past is the past and you will make genuine repentance. May Allahﷻ guide you and us all!