No particular dress has been prescribed for women as Ihram. Their usual clothes are enough provided they cover the body appropriately and are modest.
For men, it is prohibited to cover their head and face. For women, only covering their face is prohibited. Before Non-Mahram people, women might use such veils to cover their faces in which cloth does not touch the face.
When deciding to wear the Ihram, remove excess hair (as hair cannot be removed once in Ihram) and take a complete bath. Women, even if they are in their menses should take a bath. Then cover the head with the chador of the Ihram and offer 2 Raka’at Salaat (at a time when offering Salaat is not Makruh like sunrise, sunset and high noon). In the 1st Raka’at, Surah Kafiroon, in the 2nd Surah Ikhlas should be recited. After completion of the Salaat, remove the covering of the head, face the Qiblah and make the Niyyah (intention) of Umrah. Niyyah is to make a (firm) intention with the heart, but still actually saying it is also Mustahab (commendable).