A woman traveling between cities without a Mahram

Q: My sister is 30 years old. My uncle, her legal guardian, gave her permission to travel without a Mahram (spouse or permanently unmarriageable relative) to Riyadh ordering her to stay with her sister's husband, who is not a Shar`y (Islamic legal) Mahram to her. Is this legally permissible when she has a living full brother (myself)? Please, give me your legal opinion on this issue, may Allah protect you.

A: It is impermissible for a woman to travel without a Mahram. It is also impermissible for her to stay in seclusion with a person who is not a Mahram to her. Moreover, she has to stay at the house of a person who is Mahram to her so that she may feel safe. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.