Sinon could only retrieve it because of the skill/magic she used.

They really needed somebody to be a healer. I don't think she specializes in healing, but she's probably just the best on their team at it. Also, just because swordfighting was the only way to play SAO doesn't mean someone wouldn't try out other types of classes in a new game.
And she's proven she'll run up and fight when she needs to.