A few thoughts:
Lots of kids go through a fear of the dark. If you let your daughter know it's common and kids all around the world survive it every night without harm until they get over it, she may feel less alone at night.
If you empathize with your daughter, neither telling her she shouldn't have the fear, nor trying to convince her that there is nothing to fear, she's more likely going to deal with it better. If you insist there's nothing in the dark shadows, and she knows there is, then her trust in your good judgement may be weakened. (It's fine to tell her that you trust her to get over the fear when she's ready.)
A night light is no more likely to feed the fear than any other device, like Monster Spray or soothing music. Anything that can give her a sense of control is likely to help, and she'll probably only need it for a couple of months before this phase passes. Since a light is a solution that she finds appealing, a night light, or a flashlight beside her bed, might help her feel calm and in control. (When my grandson was struck with fear of the dark, the green eye of the baby monitor became a monster eye watching him, and he didn't want it on.)
She might appreciate it if you sit with her during the day and write down all the ideas the two of you can come up with to help her cope with her fear. Night light, check. Monster Spray, check (plain water in a spray bottle with a fancy label will work). Sleep with mom, check (This is only a brainstorming list – just write it down IF she says it, and eliminate it from the final lineup.) Mom sleeps with me, check. Blanket tent, check. Fierce, protective stuffed animal, check. Prayer or blessing before bed, check. And so forth, check.
Then go through the list and find two or three mutually agreeable solutions. Be sure at least one of them is her contribution – when kids "own" the solution, it will generally work better. Again, a nightlight is not a bad idea, and is less likely to feed her fear than requiring her to lay frightened in the dark.
Once a solution is found, she'll be able to more calmly observe that nothing is hurting her, night after night, and she'll start to relax. I clearly remember this phase around 4. My mom wanted me to be a big, brave girl and tough it out. My dear, dear Granny convinced her to let me have a flashlight – or maybe she just snuck it in to me. I probably didn't need to turn it on more than a few times the first night or two. I never caught the monster I was so certain was about to pounce. Then I was fine.