Is it permissible for a woman in a state of ihram for Umrah to uncover her hair and take off her abaya in Jeddah before performing Umrah, knowing that she will be staying in an apartment away from non-mahram men?

There is no objection to a woman removing her abaya and uncovering her hair after entering into ihram for Umrah, as this is not among the prohibitions of ihram. The prohibitions of ihram are seven, applying to both men and women: shaving hair, clipping nails, using perfume, hunting, contracting marriage, engaging in sexual intercourse, and intimately touching women. Two prohibitions are specific to men: wearing sewn garments and covering the head. Two prohibitions are specific to women: wearing the niqab and wearing gloves.