I totally feel your pain because I've had the exact same issue with my 2 1/2 year old and I have posted a question almost identical to yours. She was doing fine until about a month ago when the lighting outside changed again. I have tried every "trick" in the book and I too have the room darkened, use noise machines etc... I have a child lock on the door since she isn't potty trained yet so she can't come out on her own, but she just bangs on the door and yells for me when she wakes up before 6am.
The one thing that worked for awhile was setting up a light on a timer. When she went to bed at night we talked about how she could not bang on the door/come out of her room until the light came on in the morning. The first few days she didn't get it, and we had a few tears when I would not get her until the light came on. On the first day, I went in her room and sat with her until the light came on. I set it at 6:00am initially and then progressively made it later. Eventually she realized that I was not lying and that I really would come get her right when her light came on. This worked for a month or so, but then she figured out how to mess with the timer and I haven't fixed it yet or found a new place to put it where she can't reach it yet.
Another strategy might be starting "sleep rules" at night. You can make a sign/poster with your daughter about what rules she needs to follow at night and in the morning (stay in bed, close eyes, wait until light comes on in the morning etc...) Then fill a jar with a bunch of brightly colored marbles. If she follows her sleep rules she keeps her marbles. If she doesn't you can remove a marble. Or you can do it the opposite way and give her a marble to put in her jar if she follows her rules and don't give her one if she doesn't. At the end of the week if she has a certain number of marbles she gets a reward of some sort.