S.H.
A child, at certain age junctures, develops general "fears." Which is age based. My daughter and son go through that too. And they are overall well adjusted, confident kids.
The main thing is, don't make them feel like "scaredy cats" or to feel wrong about it. But let them express themselves and have validation.
They grow out of it.
But if something is really "wrong" and is causing her fears, then evaluate that... and perhaps talk with her. She most likely will not have a specific reason. But that's okay. The main thing being, that she know someone cares and talks to her about it... and she is loved.
Next, the book "Your 4 Year Old" is really great. (or "Your 5 Year Old" etc.) From www.amazon.com Although written years ago, it is still very pertinent and helpful in describing the age of a child and what they go through developmentally. Its an easy read. But real enlightening. It is a series for each age.
Again, my kids (and my kids are 7 and 3.5 years old), go through that too. Especially when it is night time. Kids have active imaginations and we can't exactly turn "off" their minds.
I give my kids flashlights to use anytime and to keep near them in bed too.
I remember as a child, feeling like that too... and being afraid of going to certain rooms by myself, even though there was no "logical" reason for it. And yes, scared of "monsters" and stuff. I was like that. Many kids are at certain ages. And my kids too. REGARDLESS of what we watch or not at home and regardless of how sheltered a kid is or not. It is just age-related development.
All the best,
Susan