Who is worthy of the title "Murabbi" (educator/guardian)? And is it permissible for this person to be other than the parents, especially if the Murabbi is a man and the one being educated/guarded is a girl? If it is permissible, what are the boundaries between them?

The function of prophets and messengers is to guide people with the religion of God and to nurture them upon it. It is a prerequisite for anyone undertaking this task to be a "Rabbani," meaning firmly adhering to God's revelation. The Rabbaniyyun are scholars who act upon their knowledge and excel in guiding people through it. The educator must strive to save people from the Fire, and the upbringing of women should primarily begin in their homes, and through righteous female relatives and neighbors. It is not permissible for a girl to have a direct relationship with a non-mahram man, even if he is a shaykh or an educator. And whoever fears God, He will grant him a criterion (to distinguish between right and wrong).