Hold up, who's this girl again? When Blanche bursts in at the end of Book III, it's Emily all over again. The poetic soul, the love for nature, and the dangerous curiosity are all there in the Count de Villeforte's only daughter. When she sees Chateau-Le-Blanc for the first time, she fancies herself approaching a castle like one in a "romantic fiction" (3.10.9). Yep, she's got Emily's tendencies, all right.
Annette was starting to get a little too silly for Em, so it's a good thing Blanche came along. Seriously, Blanche also benefits from the close friendship she has with Miss St. Aubert:
"And you know, my dear sir, how delighted I shall be with such a companion; for, at present, I have no friend […]" (3.12.1)
Both girls share an unnatural love for all things macabre, like the creepy story of the late Marchioness.
It's the classic chicken-and-egg dilemma: did Blanche's imagination start going into overdrive before or after she started hanging out with Em? Sure, it might not help that Blanche is now buddies with a girl who was held captive in a remote Italian castle. Em's adventures serve as inspiration, if you will, for Blanche's romantic thoughts.