I recently noticed that concept artworks of Alessa's revenge scene show a different origin of the barbed wire than was shown in the final film. In the movie, the barbed wire comes out of the back of Alessa's hospital bed, writhing around to in front of the bed and attacking the cultists. However, in concept artworks, the barbed wire actually appears to be coming out of Alessa's own body
. Three sections of barbed wire are depicted, with two of them coming out of Alessa's ribcage area, and the largest section of barbed wire appears to emanate from her genital region. One of the artworks in particular makes it clear that all of the barbed wire that rapes Christabella is coming from Alessa's genitals, while the strands from her sides simply hold Christabella in place.
This would be an obvious allusion to her rape at the hands of the janitor, which was facilitated by the cultists and their children. However, I believe the major symbolism would be to show that Alessa is "impure", her once innocent soul having become corrupted by hate and pain. Thus, Alessa would be removing Christabella's purity with her own impurity. It could also tie into the motherhood theme that is so prevalent throughout the movie; Alessa is, in a sense, "giving birth" to the destruction of the cult.
I'm assuming this never made it into the movie because the censors would probably be very harsh on such a scene.