If the reality is as you mentioned that
she vowed to observe Sawm, but (Part No. 23; Page No. 202) was unable to fulfill the vow, she must offer Kaffarah (expiation). It is sufficient for her to feed ten Miskins (needy persons) by giving each of them half a Sa` (1 Sa`=3 kg. Approx.) of wheat, dates, rice, corn, or any of the staple food that one feeds their family.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.