I used to be like this too.........
I used to lie in bed super-still trying to convince myself that any burgular would think I was just a doll in the bed (OK, looking back, I realise just how weird this was)
Leaving a light on really helped me, as did listening to something (like a radio or something - For me, it couldn't be something like a tape, it had to be real people in real time, IYSWIM)
Also, not sending her to bed on her own ( I always had to go to bed alone, and my 'terror' started before I got into bed) My sister used to tell me to think nice thoughts, but that never worked for me....
Taking my mind off it did......
BTW, I now sleep on my own most nights, but do so with the dog on the bed, blinds open (I never close bedroom curtains and am lucky not to be overlooked!) and with the radio on........
Hope that helps...
(My DSDs are older now... The elder girl likes to sleep with her door shut and lights off, whereas the little one needs her door open and lights on.... I think it's important to see what your DD would like and if she can pin point any thing that makes her scared..........)