A girl asks her mother why she can't keep a catalogue and is told:
I'm going to buy the year end presents tomorrow afternoon, so I'll use that (catalogue) as a reference.
How should I parse the part in bold? Why is it not それが参考にするの
I'm familiar with the idea of replacing が with の in relative clauses to move the emphasis away from the thing marked by が. But, the only way I can make a relative clause is if the の at the end of the sentence is something other than the explanatory の, which seems unlikely. What am I failing to understand?