Sydney is an independent mercenary who specializes in obtaining relics. She prefers going for the more dangerous scores (like the Declaration of Independence) and takes risks. She is beautiful, but finds men approaching her irritating. She is a loner. She prefers not speaking about her dark past. When she was very young, her mother was raped and killed by raiders. She spent years perfecting her combat skills and never welshes on a deal.
As a child, Sydney was orphaned when her father was killed during a weapons trade off at the Statesman Hotel. She had to wander D.C. alone, but she was able to handle herself because her father had taught her how to handle and maintain guns, and to upgrade them since she was young. Sydney then became a relic hunter and did some work for Abraham Washington. In her own words: "After he loaded me up with caps, I got piss drunk, got laid and was happy for the first time in a while. I haven't looked back since."
A note from Little Moonbeam's father is a note Sydney's father left her when he was dying in the Statesman Hotel. If given it to her after she tells her story, she will give the Lone Wanderer her 10mm "Ultra" SMG.(This process can be repeated as many times as one likes. Simply reselecting the conversation option about Sydney's father gives the player character access to an infinite supply of Sydney's 10mm "Ultra" SMGs.)
If Sydney remains alive at the end of the quest, she will travel from Rivet City to the Ninth Circle in Underworld and set up shop as a vendor, stating that she likes to hang out at Underworld because the ghouls do not constantly hit on her.
If the player character enters combat with the residents of Underworld while Sydney is a vendor there, she will fight on their side, unless they intentionally (or accidentally) attack her.
She can be very helpful in exploring the ruins of D.C. at lower levels, especially when used in conjunction with other companions such as Dogmeat and Charon due to their lack of a Karma requirement. However, it is advisable to carry a sizable supply of stimpaks to keep her healed through dialog, and to watch her health carefully, as unlike a permanent companion she does not automatically regenerate health.
It is possible to pickpocket and reverse-pickpocket Sydney for items, after the super mutant attack, but before speaking to her. However, once recruiting her as a companion, pickpocketing or reverse-pickpocketing her is not possible until Stealing Independence is concluded with Sydney surviving. Also, if one decides to give her a different weapon other than Sydney's 10mm "Ultra" SMG, she will use up any ammunition given to her.
Sydney is a reference to the character Sydney Fox from the TV show Relic Hunter.
She is called "My little moonbeam" by her father. However, in the Spanish edition, it became "Mi rayito de sol," which correctly translates, from Spanish to "My little sunbeam." The reason for the change is unclear, as it could just as easily have been: "Mi rayito de luna: My little moonbeam."