I led a lone non-mahram woman in salaatu-z-zuhr in our school meditation room without anyone else in the prayer from the beginning to the end. There was a Christian person seated in the same room, though. What is my fault if any?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

There is no harm for a man to lead a marriageable woman in prayer provided one is safe from being tempted by her and is not in seclusion with her, by the presence of another person [or other persons] in a way that they do no find themselves in seclusion, and the woman should stand behind the man, otherwise it will be forbidden.

For more benefit, please refer to Fatwa 88521.

Allaah Knows best.