Praise be to Allah.
Allaah says about the Muslim womans hijaab (interpretation of the meaning): and not to reveal their adornment except to their husbands, their fathers, their husbands fathers, their sons, their husbands sons, their brothers or their brothers sons, or their sisters sons, or their women [al-Noor 24:31]
The scholars differ as to whether kaafir women are included in the phrase or their women. The aayah gives Muslim women permission to remove their hijaab in front of their women. Some scholars say that the pronoun hinna (their) is referring to specific people, otherwise there would be no need to be so specific. Al-Qurtubi (may Allaah have mercy on him) said, Or their women means the Muslim women it excludes the mushrik women whether they are of ahl al-dhimmah (non-Muslims living peacefully under Islamic rule) or others. It is not permitted for a believing woman to uncover any of her body in front of a mushrik woman unless she is a slave belonging to her.(Al-Jaami li Ahkaam al-Quraan, 12/233). Ibn Katheer said something similar in his Tafseer.
This is the opinion of the Hanafis, Maalikis and Shaafais, and is one of two opinions narrated from Imaam Ahmad, may Allaah have mercy on him. Some of the scholars thought that the pronoun in the phrase or their women did not mean that Muslim women should take off their hijaab in front of Muslim women but not mushrik and kaafir women. This is the correct view of the Hanbalis. They said: The phrase or their women applies to all women, and the pronoun hinna was added because of the context and pattern of the passage, which mentions their fathers, their sons, etc. So the pronoun is added to make this word match the others.
The majority of scholars say that it is forbidden for a kaafir woman to look at a Muslim woman without hijaab, and this is the most correct interpretation of the aayah. If all women were meant, the aayah would have read or the women (in general), but what it actually says is or their women. There is no word or phrase in the Quraan that does not carry a specific meaning, and there is no evidence to support the idea that the pronoun is only there to make the word match the pattern of the rest of the passage. And Allaah knows best.