Hi Cricket
you must be feeling pretty frustrated. I give my 2yr old a spoon or two of honey when he has a cough as it helps soothe the throat. i also will give warm lemon/orange drink before bed.
Does ypur DD have some water next to her bed - i know i sometimes get a scratchy cough & water is the thing that helps calm it - its sorta like having a bit of dust stuck there.
HTH and hope your DD gets over her cough soon