To see things from 'Bitch A's' perspective; 'Bitch A' has been in this for five entire years. That means she's been training to be an idol since she was fifteen years old. Bitch A has skin in the game, and I can understand why she'd be angry here. Some upstart rookie with a pretty face just naively walked into the level 50 dungeon that Bitch A has spent a quarter of her life fighting in, as if all of the work Bitch A has put in for the past five years doesn't matter in the face of good genes.
Though, spending 5 years in a dungeon and not getting anywhere has probably given Bitch A an inferiority complex. That's likely why Bitch A is A Bitch here.