What is the ruling on a Muslim girl residing alone in a foreign country for the purpose of study and acquiring knowledge, knowing that she wears the hijab and has righteous companionship there?

It is not permissible for a woman to travel without a mahram, based on the Prophet's (peace be upon him) saying: "It is not permissible for a woman to travel for three [days] unless she has a dhū maḥram with her." A woman's travel for study without a mahram is forbidden by Islamic law, especially to a non-Islamic country. The justifications mentioned for travel (seeking knowledge, wearing hijab, having good company) are not sufficient. She must repent and return to her country.