More specifically, Nobu is thinking of an old expression about a duck appearing before you carrying an onion leek (the Pokémon, Farfetched, is based on this saying).
The saying basically refers to a super fortunate scenario as something already good came your way with extra benefits (in this case, a duck you can eat and it's carrying a leek you can use as garnish).
She basically thinks of the new Lancer as prey the brought it's own flavoring (the Divinity that makes her extra vulnerable to Berserker Nobu).
