According to long-standing folk tradition, we all have shoulder angels and devils; personifications of our own good and evil sides. They "appear" whenever we face a moral dilemma and offer advice on how to resolve it; we then choose which advice to take. This trope has classically been used in theatre as a means to portray a character's inner dialog to the audience without engaging in a monologue. Nowadays it mostly serves as a form of parody or comic-relief, though even then its allegorical nature is instantly recognizable. Even so, the trope still appears in serious works, such as The Screwtape Letters by C. S. Lewis, wherein the classical roles are reinterpreted in the forms of the Tempter and the Guardian Angel. Even so, for the vast majority of people this trope remains metaphorical. After all, no one ever actually sees these personifications.
In the world of Sir Differel Van Helsing, however, the allegorical battle between Good and Evil takes on a more personal and concrete form. Furthermore, she has many enemies who wish to destroy her, or corrupt her and turn her to their cause. It therefore should be no surprise that one would impersonate this trope and actually appear to her in person.