A. Bismillah was-salat was-salam `ala rasulillah:
It should be noted that the hadith of the three days does not mean in the understanding of the fuqaha' that she is allowed to travel alone for one day or two or up to three. The prohibition is absolute, as expressed explicitly in the hadith in Bukhari: "Women are not to travel except with a Mahram" and this takes precedence over the hadith of the three days. This is stated by Nawawi in Sharh Sahih Muslim and is confirmed by the fact that no one has considered permissible woman's travel alone whether for up to three days or for as little as one.
Other than what is stated from the Hanafi madhhab in the Reliance, the only dispensations I have seen for a woman to travel alone are:
- In going to her obligatory Hajj if the road is safe. This is "safar al-darura." See Nawawi in Sharh al-Muhadhdhab and Sharh Sahih Muslim, and Ibn Hajar in Fath al-Bari, Kitab jaza' al-sayd ch. 26 (Women's pilgrimage), in commenting the hadith: "Women are not to travel except with a Mahram."
- If she is a non-Muslim who became Muslim, or a slave who was freed, and or a Muslim woman escaping from Dar al-kufr. See Fath al-Bari, 1989 ed. 4:93, al-Mughni 1994 ed. 3:168, and Nayl al- awtar 4:291.
Otherwise the woman's travel is haram and becomes halal only on condition that she travel with her husband, or a male Muslim mahram such as her father, her son, or her brother; or at least one trustworthy woman. This is the overall view of the fuqaha'.
However: A woman travelling by plane is safe in her property and religion by all means. Therefore this issue must be pursued and a fatwa should be sought from one of the qualified fuqaha' in the matter. It should be borne in mind also that plane travel has shortedned distances and time considerably. Other factors can be taken into consideration, such as that she is travelling to a Muslim land, perhaps to visit her parents or relatives? and then returning to her husband. And Allah knows best.
Blessings and peace on the Prophet, his Family, and his Companions.