Does she sleep better if one of the parent's sleeps with her? I used to sleep with Hammerite quite a lot when she went thru phases of disturbed nights. I could never bear to leave her to cry herself to sleep - I'd much rather cuddle her. If its company that she wants while she sleeps why deny it? You can end up with a wonderful bond.
Would sound help - a monotonous repetitive sound can help little ones fall asleep (not folk then...).
Does she fall asleep on car journeys? If she'd fall into a deep sleep & sleep thru being brought back indoors it might be worth driving round a bit to get her to sleep. I've never had to do that, but I have heard of people who did it successfully.
Hope she settles down.

KRis

Kris