She must gather the scattered exposure of the private parts; for example, if one-sixth of her hair is exposed, one-sixth of her belly, and one-sixth of her thigh, they are combined. If this amounts to a quarter of any of these body parts, it would invalidate the prayer; otherwise, it does not. Refer to: Maraqi al-Falah p. 210-211, Al-Wiqayah and its explanation by Sadr al-Shari'ah 1: 143, Radd al-Muhtar 1: 408, Bada'i al-Sana'i 1: 117, and Al-Hadiyyah al-Alaiyyah p. 72.