The issue of a woman traveling without mahram is very debatable, owing to the various risks involved. Scholars are on two views; some of them permit it provided that security for a woman is guaranteed, while other scholars deemed it impermissible for a woman to travel without mahram because of the hadiths of the Prophet (peace be upon him) in this concern.
In his response to your question, sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, stated,
A girl can travel in the company of other women or when she can be reasonably assured of her own safety. This is the ruling of Imams such as Malik and Shafi; this is also the understanding of the Prophet’s own beloved wife ‘Aishah.
So, if she has reasonably believes that she will be safe and secure during her journey, then she is allowed to travel, if there is a need for her to do so.
The Prophet (peace and blessings be upon him) also said, as reported by ‘Adiyy ibn Hatim, that a woman would be able to travel all by herself without any fear of molestation from Hirah (city in Iraq) to the Haram (Mekkah).
In other words, the ban on woman traveling without a mahram was primarily because of fear for her safety. So once there is reasonable assurance of a woman’s safety, then she may travel if needed.