Someone did an analysis of the scene at the beginning of this chapter from the point of view of Yamada, because we never get to read Yamada's thoughts the only thing we have to understand how she feels is the art, you can see that she is a little concern because she doesn't know the person who he is eating with is, she stops shacking the chicken when they start talking because she wants to hear them, and she only starts eating when she hears that she is his sister, but
she is not in love with him yet. There are still some chapters left until that happen.
You are going to see the face she did in page 7 again in a later chapter. it's a nice face.