Kuro can't register her true beauty of years instilling in her mind that she will never be good enough that its so stuck up there but in this case, its not so much on thinking she not beautiful enough but she not worthy enough to be someone that nanaki can actually like. So she instinctively pairs her with someone kuro thinks is up her caliber which is Izumi. I could be wrong and kuro just had set some standard of how nanaki is in her head and really has no shred of romantic feelings. Let's hope its the first one.