Is it permissible for a woman in the women's prayer area, which is separate from the men's, to remove her head covering or to wear makeup and adornments, and are there special etiquettes of the mosque that prohibit this?

If the women's prayer area is separate and veiled from the sight of non-mahram men, it is permissible for a woman to remove her head covering and display her adornments (such as henna and kohl) within it. This does not contradict the etiquette of the mosque. However, they must be careful not to expose body parts that are forbidden to be uncovered by Islamic law. A woman's 'awrah in front of another woman is the area between the navel and the knee, and there should be no leniency regarding this, based on the Prophet, peace and blessings be upon him, who said: "A man should not look at the 'awrah of a man, nor should a woman look at the 'awrah of a woman."