Because Sister Claire is full of homages to other media. As a longtime fan, the artist, Yamino is constantly slipping in nods to her favourite media. Star Wars, Big O, Avatar: The Last Airbender and Legend of Korra, Harry Potter, Rose of Versailles, Panty & Stocking with Garterbelt, Utena, the Bat-family (Batman, Batwoman, Batgirl, Robin etc.), Mario games, Sailor Moon, Snorks, Azumanga Daioh and even other webcomics have references throughout the comic.
A lot of comics and other media are full of shoutouts. In Farscape a running gag is John Crichton constantly making media references no one else gets to stay sane. Hercules/Xena used this regularly for comic effect. Deadpool comics are full of fourth-wall-breaking references to DC comics and other media. Big Bang Theory is almost nothing but references with a laugh track. Looney Tunes and its spinoffs (Tiny Toons, Animaniacs, etc.) referential inserts far outweighed its original content.
It is the nature of media to incorporate other media to act as cultural reference points. And media created by fans is far more likely to do this, especially if their audience is other fans.
Other Star Wars nods include:
- Energia - Analogous to the force, that both the Nuns and Witches wield in different ways similar to Jedi and Sith. It binds all living things together
- Title of Chapter 7 borrows from Luke training on Dagobah.
- The mystery around Clair's birth and destiny making her analogous to Anakin.
- And of course Sister Yolanda
All in all the Star Wars references are a little less prevalent than say Avatar, or Rose of Versailles but they are there.