A woman with some sort of mental disorder said: O Messenger of Allah, I need your help in a certain matter. He said: O Mother of so-and-so, choose which road you would like (to meet me on) so that I may give you the help you need

A woman known to be mentally unstable said to the Prophet (may Allah's peace and blessings be upon him) that she needed his help. He asked her to choose a road on which they can meet so that he would help her with what she needed. He then stood aside with her on a much-trodden road until he gave her the help she needed.

Needless to say, this was not forbidden seclusion with a non-Mahram woman, because the Prophet (may Allah's peace and blessings be upon him) stood aside with her on a much-trodden road where people could see them both but without hearing the woman’s speech (out of respect for her privacy). This behavior shows how humble and compassionate the Prophet (may Allah's peace and blessings be upon him) was towards his followers.