What is the ruling on a woman wearing a belt around her waist over a jalabiya or blouses, and can the action of Asma bint Abi Bakr (Dhat An-Nitaqayn - "Possessor of the Two Waistbands") be used as evidence for its permissibility?

It is not possible to infer the permissibility of uncovering the face from the story of Dhāt al-Niqāṭayn (the woman with the two waist-wrappers), for the niṭāq (waist-wrapper) is a garment a woman wears in her home for service. Asmāʾ Dhāt al-Niqāṭayn would lift the food for the Messenger of Allah, peace and blessings be upon him, and Abu Bakr with it, and she would tie it around her waist. Furthermore, the story of the two waist-wrappers occurred before the Hijrah (migration), whereas the hijab was enjoined in Medina.