Hi, D.. Well, there is no simple answer that will work for everyone. However, I think that if your daughter is scared, a little bitty night light left on during the night will not hurt her at all. You might want to see if she is getting more teeth and that is waking her up, or maybe her stomach is bothering her.
Try also to shorten her naps during the day so that she will need more sleep at night. Wake her from her nap ten minutes earlier than usual to start with so that she will not really notice the change, and then gradually take away another few minutes until she is sleeping about 30 minutes less for her nap than she was before. Her body will then cause her to sleep more soundly at other times, like during the night.
Children around this age can start developing sleep terrors and nightmares. You might want to read her books about "monsters" that are not really scary, such as Sesame Street monsters like Cookie Monster who don't hurt anyone. Maybe this will help her to stop being afraid of things like shadows when her mind forms them into weird shapes in the dark.
You might also want to talk to her about fear and what it means. Also talk to her about dreams, and how they can't hurt you no matter what happens in the dream -- it's just a story. Children of this age are not able to tell the difference very well between fantasy/dreams/thoughts and reality, so this may be an excellent time to introduce to her the concept that some things are just stories or make-believe. In other words, thoughts and dreams are just another way to play. You could try joining in with her when she is playing pretend, like letting her be pretend-mommy and you being pretend-daughter or something like that, and then maybe acting out something that you read together in a book, and then showing her that that is like what happens in dreams -- and try to make thoughts pleasant instead of letting them be scary.
Anyway, I hope this is helpful.
Peace,
Syl