I'd put good money on Sylvie being a red herring and it actually being Nick Cotton. It makes sense as this week has mainly been centered around the Carter's and the Butchers, whom have been interacting more than evenlr recently what with Carol and Charlie, Whitney and Lee and the drugs.
I don't doubt that Sylvie will turn up, she probably will around Christmas time to reveal the truth about Mick's parentage, but I think her being Aunt Babe's roommate is a bit too obvious for my liking.