How does the author use foreshadowing in If There Be Thorns?

In Part I, Cathy tells Jory that she's "compelled" to dance in the attic, despite the dust there and the fact that there's a ballet barre downstairs. When Chris finds her there, he's always angry and Jory doesn't understand this, though it's a foreshadowing of the story that will emerge - that Cathy and Chris had been locked in an attic for a long time during their childhoods.