Subordination is linking two clauses in a sentence so that one clause is subordinate to (or dependent on) another.
In subordination, a subordinate clause is attached to the main clause with the help of a subordinating conjunction.
There are many subordinating conjunctions. That is one of them. It introduces the attributive clause <em>that showed her interest in science</em>. The attributive clause refers to the noun <em>books </em>in the main clause 'Lupe’s room was full of books'.
