Is a woman considered a mahram for another woman who is not a relative during travel and similar situations?

A woman is not a mahram (definition) for another woman. Rather, the mahram is the man to whom a woman is forbidden [to marry] by lineage or a permissible cause. It is not permissible for a man to be alone with a foreign woman or to travel with her, due to the Prophet’s (peace and blessings be upon him) saying: "A woman should not travel except with a mahram," and his saying: "No man should be alone with a woman, for verily, Satan is their third."