What is her current sleep schedule? My DD wakes around 6:30, usually naps around 1 for an hour, then doesn't fall asleep til 8:30/9pm (we do bedtime at 7:30/8). She is starting to resist the nap, so today we let her go without it, and will leave her room from putting her to bed at 7 (that is the aim).
Another thing that we do, which gets her relaxing in the first place, and also helped to start the reading to herself habit, is we read to both kids, then leave her to read alone while we go put our baby to bed (well I do LOL) and then we return for the big girl story. Before we leave we talk about the big girl story, and that she needs to wait until we return to read it, and she usually winds down well before we return, then we read that story then leave.
We used to always have our DD in pitch black (spirited) but now she has both a night light AND the door open, so heaps of light. We have a night light on in the house when we go to bed too, in case she wants to wander in to us. The light does not prevent her sleeping, and makes reading in bed before she falls asleep more comfortable for her.