If she prays and any part of her ???awrah becomes uncovered, such as a shin or foot or all or part of her head, then her prayer is invalid, because the Prophet said: Allaah will not accept the prayer of a woman who has started to menstruate, except with a khimaar (covering) (Reported by Ahmad, Abu Dawud, Ibn Maajah and al-Tirmidhi, with a saheeh isnaad)