Thinking about how the young girl lectures the robot about how love is more complicated and difficult, I wonder if she realized on some level that the "beautiful and pure relationship" the old ladies had was actually a romantic one before the kiss even happened. Certainly that was confirmation, which is why she kisses the doll afterwards, but I'm pretty sure she suspected it was more than simple friendship.
In their youth, those two must have been straight out of Marimite, though.