Take it away. She shouldn't be doing this. She is not getting quality sleep, and there is simply no reason for her to need this. Using electronics is NOT self-soothing. It's not even close. Self soothing is falling back asleep by your SELF, not yourself and an electronic.
You need to hide them, and not accept this behavior any longer. Common sense mom, this is a BAD habit and idea.
ETA: I wanted to add, I would NEVER allow my child to have free access to these electronics. They have the internet. Do you know how easy it is, to find inappropriate things on the internet? I was on my tablet, trying to check mamapedia. I wasn't paying attention and typed the url wrong, and guess what popped up? Serious pornography. Not only that, predators are all over the place. What about in 5 years, when she is doing the same thing? Do you REALLY want a preteen/teen, to be on the internet in the middle of the night? There is too much temptation, and bad people waiting to take advantage of young girls. YOU need to be the parent and set up some serious boundaries with your child. If nothing else, to simply protect her.