It was a night course not OW
I am still struggling why her light was not visible on the surface. Even if it were comparatively weak this is not deep at all. And lights are easily seen here even in poor vis from much deeper than the honeybear. If her light failed and that triggered some sort of panic that is obviously a different story
The SDI standards for Night/Low Viz training require a light and a backup light. I would think that other agencies would require the same thing. This is not a comment to start an agency fight. I have only trained with SDI/TDI, so I'm naming the agency simply to say that it is the only agency standards that I know.
I have taught some Night/Low Viz dives. It is not a required skill to make the students handle a "failed light". This thread does make me give some thought to whether I should incorporate that into the start of every Night/Low Viz dive #1 from now on. In other words, at the start of the first Night Diver class dive, make sure each student can successfully deploy and use their backup light before proceeding any further with their dive.