Does the day a woman fasted to make up for Ramadan, and she doubted whether she broke her fast five minutes before sunset, count as a day of making up, or must she repeat it?

Mere doubt about breaking the fast before sunset is not to be heeded, and making up the fast is only obligatory with absolute certainty, because doubt after completing an act of worship has no effect, due to the hardship and difficulty it would entail.

However, if there is certainty about breaking the fast before the time, then making up the fast is obligatory according to the majority of scholars, as Umar ibn al-Khattab (may Allah be pleased with him) did when he broke his fast, thinking the sun had set, but then it became clear that it had not. He said: "The matter is easy, and we have exercised ijtihad," meaning they would make up a day in its place. There are proofs for the view that making up the fast is not obligatory, but the view of the majority is more cautious and more absolving of responsibility.