Hi, S.,
I was a child similar to your daughter, and I had a genuine fear of the dark. Thankfully, my mom and dad were not concerned that I would get used to something that others might have considered "unhealthy" or "odd". I had a nightlight bright enough to make everything in my room recognizable (this was very important), and they left on the hallway light with my bedroom door open until they all went to bed, which was always a few hours after I did. If I was afraid in the middle of the night, I was allowed to go sleep in my sister's room, who was not afraid of the dark.
As I grew older, my fear subsided, and my need for a nighlight, etc. lessened as well. However, it is still my nature to be uncomfortable in the complete darkness. A small light is always a comfort to me. I think that had my parents decided that I should just learn to be comfortable in the dark or not be afraid at night, I would have become even more fearful of it.
Anyhow, just my persoal experience with this situation. I hope it's helpful.
L.