As an omen, the fact that Enzo brings up crows right after talking about Eve's worsening conditioning also seems like some pretty obvious foreshadowing to us. We also wonder whether it's a coincidence that angry crows and ravens, omens of death, are specifically mentioned in Chapter 13? Not that we're superstitious, or anything.

In this instance, it's not the distance that Denny is traveling that Eve is worried about—she's worried that she won't be able to keep the illness at bay when he's gone, and that she doesn't know how to fend for herself, taking care of a child and a dog alone, while also suffering this sporadic, crippling pain. She needs Denny, but she also promised she would be oaky if he left. So she has to keep that promise.

Denny is sensitive of Eve's needs, and he knows that in some ways he is helpless when her illness takes her, so he asks Enzo to act as intermediary, because it's all he can do. It's back to that theme of control: understanding when you can and can't act, and doing what you can in the meantime.