I say, and with God's success: If a fasting woman has her period during the day, if it is at the end of the day, her fast is invalidated, and she must make up for it if it was a mandatory or voluntary fast. There is a difference between them as stated by Sadr al-Shari'ah in Sharh al-Wiqayah, p. 124, where he did not require making up for a voluntary fast. Ibn Najim refuted this in Al-Bahr 1: 216, stating that there is no difference between making up for a voluntary prayer and a fast, and that what Sadr al-Shari'ah said about the difference is incorrect. This was supported by al-Haskafi in Al-Durr al-Mukhtar 1: 194, al-Laknawi in Al-‘Umda 1: 129, and Ibn Abidin in Manhal al-Waridin, p. 139; due to what is mentioned in Al-Fath, Al-Nihayah, and Al-Esbajabi regarding the lack of difference between them, and similar in Al-Durr. And God knows best.