When the 'Leverage' crew pulled off "The White Rabbit Job", Sophie Devereaux assumed the alias of "Sally Sparrow". It's a unique name, but not so unique that it doesn't already exist in Earth Prime-Time.
Sally Sparrow is a young woman in London who runs a DVD shoppe with her best friend's brother, Lawrence Nightingale. In 2007, she ran afoul of an alien race, deadly assassins known as the Weeping Angels. This eventually brought her into contact with a Gallifreyan Time Lord known as "The Doctor".
As such, I'm going to suggest that Sophie used that name because she actually knows Sally Sparrow.
If I say that they grew up together, I don't mean that they were the same age. I think they grew up in the same neighborhood and went to the same schools, but there's nearly a full generation span between them in age. I think it's pozz'ble, just pozz'ble that Sophie Devereaux - whatever her real name is - grew up with Sally's Mom (whoever she may be.)
That Sophie bandied about Sally's name so cavalierly doesn't seem to have been a concern. This is probably due to her "mark" thinking that he was seeing her in a dream. There was no fear that he'd try to investigate Sally Sparrow. If anything, he'd try learn the dream significance of her name.
As you can see from the above Tumblr gif, Sophie also bestowed an alias on one of her partners, "Mr. Steed".
Mr. Steed - at least for the Trueniverse audience - is nothing more than a tip o' the bowler to John Steed, Patrick Macnee's character with whom he is most identified since the early 1960's and into the late 1970's. Perhaps even into the 1980's - if "John Steed" was just a cover identity for the man who would eventually be in charge of U.N.C.L.E. headquarters in New York City - Sir John Raleigh. (Macnee played that role in the 'Man From U.N.C.L.E.' TV reunion movie.