What is normal hen pecking?

We have 2 chickens, a sicilian buttercup and a golden laced wyandotte. They are about 4 months old, raised together from a day or two old. They free range during the day in our fenced urban backyard (which is about 1000 square feet with grass, roses, fruit trees). They have access to food and water in their coop. Their coop is 12 square feet. They just recently switched from chick starter to layer crumbles. They get occasional kitchen scraps. We have been painting in the backyard the last few days, with red paint, and both chickens have managed to put their beaks and combs and feathers in the red. Now we have the buttercup pecking the glw...she will run at her, peck the back of her neck or around her face, and the glw cowers. Previously the glw has followed the buttercup everywhere and they have seemed inseparable. But now the buttercup is territorial, pecking the glw if she is within range, not allowing her access to the dustbath they created under the rose bushes. Even when the glw is pecking at grass, the buttercup comes up from behind and pecks her neck, grabbing feathers. So far, no blood (other than the red paint which is just on the glw's face, not her neck) and no pulled out feathers. I bought some "Pick No More," which is tar and some other ingredients, and put it on the glw. But I just watched the buttercup peck the glw, wipe her beak, peck again, wipe again, for 4 cycles. It almost seems like the Pick No More is not really deterring her. When should I worry? This is our first time raising chickens.