T.,
When I was a young child, I shared a room with my sister. She always fell asleep, I could not do so. My parents let me sing quietly to myself until I tired out. But a loud TV did bother me. I still prefer sleeping in a quiet, and sometimes dark room. Light effected me, and kept me awake. I also walked in my sleep according to my family. I played very hard during the day, but that did not help me sleep. My husband will tell you that I love to sleep now.
My mother also tried changing my eating and bath pattern too, but it didn't work. I truly could not go to sleep. I wasn't trying to stay up.
I still like to stay up late, but I do get more sleep when I can. Sleeping in is a pleasure now, and taking naps started in my teens, which I still do if I am home.
So, don't give up. You might have to move your daughter away from a wall that has the sounds of a TV or stereo coming into her room. Tell your other daughter to roll over and try to ignore her sister. I use to try to keep my sister awake because I was envious of her being able to go to sleep so easily. It didn't work, and she started going directly to sleep. Oh yes, sometimes she would sing one song with me.
I hope this helps you in someway.
E.:)