... Zack was taking care of him when all of us were off on the draft, right? He was still there at our house when I got back.

[ And thus comes the indication that she's that girl (or one of them) that lives with the dude she came in looking for. If Shizuo didn't already know that at least in part; if Zack's managed to keep his mouth completely shut about his girlfriend, she'll be ... shocked. ]