Does it seem like if she would just lie quietly for a little while she would fall asleep, but she just won't stay still or quiet without you? That's the problem I had (have) with my daughter. This is what finally worked for us...
We got the kitchen timer out, and I told my daughter that I was setting the timer, and that she needed to stay in bed and wait for me to come back when the timer rang. The attitude was that this was a little game--could she wait quietly while I went to start the laundry or whatever, until the timer rang? I started with just 2 or 3 minutes so she could see that it wasn't so long, and I really would come back. Then I put the timer in my pocket and left the room. As soon as it rang, I went back and sat with her for a minute or two. Then I explained about setting the timer again and that I would be right back when it rang. But each time, I lengthened the time by a minute or two. Eventually, I would come back and she would be asleep.
We repeated this nightly, but each night I started the timer at an extra minute or two so she would slowly get used to waiting longer for me. It took some time, but it was relatively painless, crying-wise. And eventually I didn't need the timer any more. I could just tell her that I would be back in 15 minutes or after my shower or something like that, and she would wait in bed for me. Usually she'd be asleep by the time I returned.
If she decided to get up and not wait for me, I would take her right back and possibly start the timer over again.
Now she's 5 and when I put her to bed, she says, "don't forget to check on me later." And her room is usually quiet after that because she falls asleep pretty well now. But occasionally in the morning she asks why I didn't come back, and I just have to explain that I did, but she was asleep already and praise her for being such a big girl and going to sleep so well.
We've used the kitchen timer for lots of different things, and this one worked real well. Might work for you too. Good luck!