The pattern is from Girly Style Wardrobe, and is intended as a slip to be worn under another dress, but its loose-fitting style with no closures makes it perfect for nightwear. The fabric is from Spotlight's Japanese lawn range and the trim is cotton lace (and plenty of it!).
R is thrilled with her long nightie and is now requesting a long dress - which won't be happening until she drops her demand for an off-the-shoulder style. I'm just happy she's no longer squeezing herself into a tiny torn nightie!