They don't stop pecking, but it does become less frequent. If they want a spot where another chicken is, they will peck the other chicken's tail to get her to move.
That is definitely a hen. At 16 weeks, you would see much bigger combs and wattles, as well as saddle and hackle feathers in roosters. She is likely working out the pecking order with her fellow hens, which would explain her behavior.