What must a woman do who swore upon the Quran, saying, "By Allah, if I do not marry so-and-so, then I will not marry [at all]," and she did not marry him?

If a woman marries another man after swearing an oath not to marry, she must perform an expiation for breaking an oath (feeding or clothing ten needy persons, or fasting for three days). If a suitor whose religion and character she approves of proposes to her, it is better for her to accept him and expiate her oath, as the Messenger of Allah, peace and blessings be upon him, said: "Whoever takes an oath and then sees something better than it, let him do what is better and expiate his oath." Accepting the suitor might even become obligatory if the woman fears falling into haram (definition) (unlawful acts) by rejecting him, because safeguarding oneself from haram is obligatory, and marriage is the path to achieving that.