4. 「何もありませんけれど、どうぞ。」と大島さんは言ったが、大島さんがあらかじめお寿司を注文しておいてくれたのがエイミーにもわかった。
My translation: "'I don't have anything [polite understatement], but please help yourself', said Mrs Oshima, but Amy realised that Mrs Oshima had ordered the sushi for them in advance."
Is this OK? They are at Mrs Oshima's house, so in what sense is 注文して used? Is it like ordering from a takeaway or something?