What is the ruling on the wages earned from teaching a girl to read and write without a mahram present?

A man is not permitted to seclude himself with a non-mahram woman, even for the purpose of teaching, due to the potential for corruption it entails. There are prophetic narrations that prohibit this, including: "No man is to be alone with a woman unless there is a mahram with her," and "Indeed, no man is alone with a woman except that Satan is the third of them." Unlawful seclusion (khalwa) is any private meeting where suspicion is not usually dispelled. This includes the presence of a young child who is not shy, or the gathering of men with a non-mahram woman. As for the earnings acquired from such seclusion, there is no harm in benefiting from them, as they are in exchange for a permissible service. However, teaching the girl in that manner must cease in the future unless Sharia-compliant regulations are met.