Which niche would fit for fiction writers?

Hi everybody! I came across the “Narrowing Your Niche” worksheet and was surprised by the first point: My fiction books (suspense, mostly) do not fit into the “wealth”, “health” or “relationships” categories (although every fiction story is about relationships somehow, but for me, that is not my focus, e.g. I don’t give advice on relationships). My readers are women who relax by reading suspenseful books with strong female characters and with a message that they can implement in their lives. The worksheet says “change your market”, but I can’t see how this should be possible for fiction books. Any examples or thoughts?