I don't think that it's an artifact, just they way the lens rendered the chain link. You could scan the negative and compare it to the scanned print. And I would leave it, it adds dimension. Was this taken with a Leica Summicron?(posted 8704 days ago)Do you know this girl? I am always hesitant to take photographs of kids I don't know. Maybe that's why I rarely have shots this good.
Great picture; frame it and hang it.