Making Kaffarah for an oath on behalf of another person
If the reality is as you mentioned, it is Wajib on her to make Kaffarah for the oaths
that she broke by doing what she swore by Allah not to do.
The Kaffarahs have to be as many as the broken oaths, only if the breached oaths were taken regarding different matters.
It is permissible for the man in question to make the Kaffarahs on behalf of his fiancée on a voluntary basis, but he must inform her of this.
Sitting alone with the fiancée in a separate room is
a prohibited Khulwah (being alone with a member of the opposite sex). Even if her mother is in the same flat but in a different room.
Q 2: This question also relates to oaths. A man's mother took oaths not to do a certain thing, not to go to a certain place, etc., but she then violated her oaths. Her son mentions that he may be responsible, along with some other reasons, for encouraging his mother to break her oaths. Is it permissible for the son to make Kaffarahs on behalf of his mother for the numerous oaths that she breached? It may be worth mentioning that the mother is ignorant of the rulings of Islam and her son does not think that she will make any Kaffarah. He feels somehow responsible. What should he do?
(Part No. 23; Page No. 40) A: The son has to make Kaffarah for the oaths that his mother broke as explained in our answer for the first question. He must be dutiful and kind to his mother. He has also to obey her whenever she enjoins him to do any Ma`ruf (that which is judged as good, beneficial, or fitting by Islamic law and Muslims of sound intellect).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.