In The Egypt Game, why is April at first concerned about the empty mailbox and then later concerned about Dorothea's latest letter?

With a crazed killer on the loose in the neighborhood, the kids are in lockdown. That means no going outside to play; specifically, it means no Egypt Game, at least for the time being.
As one can imagine, it's difficult for the kids being cooped up inside all day. It's especially hard for April, who, without the Egypt Game to think about, starts thinking about other things such as the empty mailbox. April hasn't heard from her mom, Dorothea, in over a month, and she's understandably concerned.
But even when April finally does receive a letter from Dorothea, there's more to worry about. Dorothea doesn't answer any of the questions that April asked her; she simply tells her daughter that she's back in Hollywood and is working in a nightclub. She also tells her about Nick. But to April's consternation, Dorothea says nothing at all about April's coming home.