Marnie's a sweet nickname name—it's usually used as a nickname for Margaret (which means pearl), or Marnina (which means joyful). It's big claim to fame is the name of one of Alfred Hitchcock's movie—where it was the name of a bit of a wild character. It fell out of the top 1000 into the 70s, but it seems poised to come back, with Marnie as a character on HBO's Girls, and on Halloweentown. It's a sweet, old-fashioned name, especially when paired with Rose, one of the hot floral middle names. And it's a nice alternative to some of the other hot nicknames, like Millie, Maddie and Maisy.
It also fits in nicely with big sister's name, another old-fashioned name—Ethel means "noble maiden," and fell out of favor around the same time as Marnie did. It's most associated with entertainer Ethel Merman, though there's currently a character (a former cult-member foster kid) on Shameless. And Mary's one of the most classic baby names, an ancient name that means "bitter," and a name that was tops for decades.
What do you think of Lily Allen's baby names? Would you choose one of them for your daughter?