Becoming a "Celestial Maiden" was an exceptionally simple process for her. She merely had to find the Celestial Maiden who had saved her before, express her gratitude and longing, and she was given a chance to test her talent. After testing, it was confirmed that she indeed possessed the innate gift to become a Celestial Maiden.
Since then, she rarely used the name "Lu Hongdou" anymore, but rather adopted the code name of her Celestial Maiden identity—Canna.
Or it could be said that "Celestial Maidens" weren't really called Celestial Maidens. The true, self-acknowledged name for this group of girls should actually be "Magical Girls."
Martial artist Lu Hongdou became Magical Girl Canna.
Of course, becoming a Magical Girl didn't mean she had abandoned martial arts. Quite the contrary, it was precisely because she had become a Magical Girl that she grew even more fanatically devoted to martial arts.