If you are referring to the highlighted text, it could be re-written as follows:
"... as I try to write a novel. It is a thought of Derrida's and very simple."
As you can see, the author expressing that
"It's Derrida" suggests that it ("it" being a reference to the
"new quote") is a thought of Derrida. For additional context, Jacques Derrida is a French philosopher who is known for developing a form of semiotic analysis (i.e. the study of signs and their meaning relating to the social world and social processes) called "deconstruction".
The quote
"If a right to a secret is not maintained then we are in a totalitarian space" is an intertextual reference used by Smith to create new meaning since she is establishing that the secrets that are obtained are ones created by the author/writer and that the reader plays a role in attempting to determine some of those secrets.
I hope this helps!