How soon after falling asleep has she been waking screaming.
Age just about 2years was the time when Matthew would wake at around 10.30 at least once a week. I put it down to night terrors? they are associated with disturbed sleep in the early stages of sleep. They appear to be awake - i had pretty coherent conversations with Matthew - or rather - he would ask for me, I'd be there but actually once I was there - he'd push me away, or perhaps he'd ask for a drink and then when i gave it - he threw the beaker across the room.
After some reasearch we found that the best way to deal with this when this happened was to go in to his room, not touch him, but just in a low voice, reassure him that mummy was here, i love you etc. AFter about 10 minutes he'd resettle and go back to sleep.
another thing that we had to try (not necessarily related to the night terrors) was sometimes we had to go back to 'resetting' him for bedtime, which meant going through the bedtime routine again of story, cuddle, count toes, godbless, turn out the light etc and then he'd go back to sleep.
all the best
Alex