What is the Sharia ruling on intervening to stop a young man walking with a girl who appears to be insane late at night? Is that considered enjoining what is right and forbidding what is wrong? And what are the limits of intervention in this case, whether the girl is willing or not?

If the girl is a stranger to the young man, then what occurred of seclusion (khalwa) and touching is a reprehensible act (munkar) that must be changed through admonition and instilling fear of Allah's punishment, for both of them. If they do not comply, and if changing it by hand would lead to a greater harm, then the guardian (wali al-amr) must be informed. For changing a reprehensible act is obligatory according to one's capability: by hand, and if unable, then by tongue, and if unable, then by heart.