It's strange that she will fall asleep with your dh and mum but not you. Maybe she is picking up on your stress around the whole sleep thing? Do you have an electric swing? I know your DD is older but when DS was little if he was having trouble drifting off we'd put him in the swing and he'd fall asleep. Even now on the odd occasion if he's having trouble we can put him in that for 10 mins and it makes him drowsy, enough to pick up, feed and then he falls asleep after that.