i'm so sorry, too. My heart still hurts from the two chickens i have lost so far. Your chicken was lucky to have you as her mom for her short time on this earth.
i think your best bet is to isolate, keep the chick calm and quiet. Try to clean the area up. Best thing is to soak her bottom in some lukewarm water until you can see what you're dealing with. From what you are saying it may be a bit of a prolapse that got pecked at. Treating for a prolapse...