Swearing to build a Masjid in front of her house if she graduates and becomes a teacher

Q: When I got married to my cousin, she told me about a vow she had made before we married. In the last year of her studies at the Institute for Female Teachers, she took an oath by Allah that if she were to graduate that year from the institute and work as a teacher, she would build a Masjid (mosque) in front of her house. Thanks to Allah, she graduated and worked as a teacher for three years but she did not build the Masjid. She is unable to do so because she has no income other than her monthly salary and the pension of her late father which is used to help her brothers who are students in preparatory and secondary schools. She is confused and does not know what to do. Is this act considered a vow or an oath? In either case, what should she do? It is noteworthy that she is unable to fulfill what she intended to do. Must she fast for three days along with feeding ten poor persons? Or would the fasting alone be sufficient? (Part No. 23; Page No. 383) Please inform us of the solution for this dilemma.

A: She must fulfill the vow by building the Masjid, if she can afford it or wait until she is able to do so. If the fulfillment of the vow is impossible, she has to offer Kaffarah (expiation) for an unfulfilled oath by feeding ten needy people, clothing them, or freeing a believing bondsman. If she cannot afford this, she has to fast for three days.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.