I wish I knew what to tell you, but I don't. However, you are not alone. I have 2 sons, ages 2 and 4. They share a bedroom and until I opened my big mouth, they were doing great. One night just as they had laid down for bed, I just happened to look out of their bedroom window. I saw a huge deer standing in our backyard, so I yelled, "Look Boys! There is a big deer out here!" My 2 year old ran to the window to see the deer, but my 4 year old ran the other way, straight to his moma. He was 3 at the time, but he has been scared since. He says that the deer is going to come through the window and get him. Now he sleeps with his moma, while I sleep in the spare bedroom. That is fine with the 2 year old though. Nothing scares him, so he has no trouble in his room all alone.

I haven't had this problem, but I have a couple of ideas.....I got a book at Halloween called "Go away Big Green Monster!" I thought it was cute to teach parts of the face and colors. The book puts the monster together part by part then you take it apart as you tell it to "Go Away" "Go Away big yellow eyes. Go away big green monster. And don't come back until I say so!" Oh jeez, I've been reading that one too much! LOL! Maybe that book or other ones about night time fears would help. I know you've tried a nightlight, but have you tried a flashlight? She could aim it at whatever was bothering her and get a clear sight of what it is (nightlights still sometimes leave bad shadows). Find one she can turn on and off. Explore her room with her with the lights off.

I don't know if books about night creatures would make things better or worse. Stellaluna is a great one for bats.

Good luck! I hope everyone gets some sleep soon!

Try adding an "inspection" to your bedtime routine. Together with the lights are on, look in all the corners, under the bed, in the closet etc. to see that there's nothing unusual there. When she calls out, go in and remind her that you checked everything, it's okay. It'll probably take some repetition but hopefully the reassurance will pay off.

Another idea, this one from my own childhood, is "Monster Spray." Cover a air freshner bottle with your own design including whatever your little one fears the most (for me it was bears and werewolves). It doesn't have to be elaborate, just something recognizable. Spray it at bedtime and tell her that it keeps all the monsters/scary creatures away. This can be repeated if she wakes up too.

Also, when my son started talking about "monsters" I reminded him that monsters can be friends, like Grover and Cookie Monster and Sully (from Monsters Inc.). I repeated this constantly for weeks. Now he reminds himself, "Monsters can be friends!" Good luck!

I wish I could give you a 100% solution but I can tell you what worked for me, my son got afraid of the dark at about the same age so I put a radio in his room so he could listen and relax to it along with a 10 watt lamp and told him monsters are afraid of music and his Spiderman lamp.
It may work for you too
Amanda