Am I just mean?

I would disregard others here attacking Nyctophobia as a childhood syndrome, I've met a couple of adults with it, including a homeless man who had to sleep directly under a street lamp in the rain, without shelter of any kind, because of his extreme fear of the dark- and he was quite muscular.

At this point she is going to need to see a therapist capable of prescribing medications. She's likely to have panic attacks if you follow people here, you don't see this in her because her brother just got used to managing the onset of symptoms, but life will suck for you if the power goes out for a few days.

Once on meds, it's baby steps, the inhibitors don't override the conditioned response, just makes it less severe when learning to cope. Is she so far gone that she is afraid of her own shadows?