Silk was the abandoned child of a pirate and a character from Romance Dawn V.1. She aided Luffy in her efforts to defeat Crescent-Moon Galley when he attempted to take over the town she was living in. She said she had heard of Red-Haired Shanks when Luffy mentioned his saviour as a child and that he was one of the most famous pirates in the world.

Several years later she is later seen on a ship alongside Crescent-Moon Galley telling her Captain (which was obviously Luffy) that land had been spotted.

Silk was Oda's first attempt at a Nami-like character. She shares much of Nami's personality, however was much more kind and seemed to boast more leadership skills rather then relying on force to make people do things. Although that could be put down to Romance V.1 Luffy being far more intelligent then the final version. Appearance wise, aside from her hair being long everything about her (including her choice style of clothing) was almost identical to Nami.

Her background story was much closer to Nami's own background story than Ann's background story was. Both girls were parentless at very young ages and both experienced their hometowns being subjected to pirate related suppression. The difference is that while Silk encouraged the townsfolk to stand up to the pirates, Nami did not want anyone to fight them through fear of someone being hurt. Coupled with this was the difference in reaction from the two hometowns - Silk's hometown did not want to fight the pirates where as Nami's were prepared to die trying.

(Source: One Piece Encyclopedia)