Why isn't a minor charged for underage drinking if they are a victim of another person breaking the law?

Why was the young lady who was the victim in the infamous Richmond high school rape incident not charged with underage drinking? In CA you have to be 21yr old to legally drink, and there is more than enough evidence to show she was inebriated with a near fatal dose of alcohol. Discounting how that facilitated or was a catalyst to the second crime; her being sexual assaulted. Should the DA follow the very letter of the law and charge every lawbreaker even if, in this case, one was a victim of the other lawbreaker?

(disclaimer)
BEFORE ANYONE GET STARTED, I am not saying the person who assaulted her should not have been charged. I am not saying the young woman deserved to have been sexually assaulted. I am not saying those who assaulted her are blameless.