Hey... that Youko... she was coming on to Nanami like a freight train. I'm not mistaken, right?
The expensive present of soap and skin products, the invitation to go out for drinks, just the two of them, and, most of all, that "bad luck on my part" comment when she finds Nanami already has someone -- all of these seem to hint at Youko feeling a romantic attraction to Nanami.
Well, I can see why she thought it could work, I mean, what with Nanami paying her so much attention lately, and all. Her face when Nanami rejects her invitation seems to be saying: "Damn, I misread the signals!" But, really, IMHO, even if there wasn't a Kaede at home, Youko wouldn't have a chance with Nanami. She's not Nanami's type.
That black-haired cutie working at Kawakami's, on the other hand, heh heh...