Since this has been going on so long, the first thing I recommend is rearranging her room, maybe even with her bed against the spot she afraid of so she is no longer facing the spot. Definitley consider the effect of lighting in the room from monitors, night lights, street lights outside, the hall, anything that might be casting an odd glow or a shadow. My son used to see awful looking moving shadows in his room that we could not see because the shadows were caused by us when we were in his sister's room in front her air purifier. It took us forever to figure out what he was seeing.
Another thing to consider... is she taking any medication? When my daughter was 3, she took Claritin allergy med. and she started having more than bad dreams. It was more like night terrors. Thank ggodness my husband had had the same reaction when had taken it years ago and recognized it as the cause (after about a week). The night terrors stopped when we changed medications.
My best advice, though, is this. I was terrified of the dark as a kid all the way until about two months after after I got married! I had even lived alone in college for two years! Someone it took my husband being away in the Marine Corps on training for me to finally get over it.
So, I vowed that no child of mine would ever be forced to sleep alone in her room if she/he was truly too afraid to do it. Seriously, what is the point in forcing a child to be terrified? It made no difference for me. As in, it didn't make me get over it by making me tough it out. So when my kids occasionally go through phases where they are afraid (usually around that awful time of Halloween or after seeing something scary when the school shows them a stupid movie) I either lie down with them until they fall back asleep or I let them sleep in my room for even a few days until they get over their fear and sleep in their own room again.
And it has always worked. It always turns out it's just a short phase they needed help getting past.