Well, both cliche I've given are possible here. And yes, you could say Как мы уже знаем (узнали, выяснили), Светлана считала... but that doesn't correspond with the style. The как мы уже знаем is a little intimate; it would fit for a tale or something like this. And the style of the story I think is dry and a bit derisive. The two cliche are perfectly fit for the style.