At those ages they are mature, it's not juvenile issues. It just started a month or two ago. Sometimes the pecking order changes. For whatever reason one chicken decides it has a chance to become top dog, the flock master. Maybe it senses a weakness in the current flock master. Maybe that Silkie rooster is so slow to mature that this has something to do with it, they have to mature to a certain point to try to take over. When I've seen this it's over in a few days, not weeks. Until it's over he would not let the other hang with the flock.
That hen is a Barred Rock, by the way.
Chasing her with hackles raised is not mating. I don't understand him pecking at her tail. Usually I'd expect him to go for the head, either to hold on for a forced mating or pecking the head to try to kill. To me it sounds like he is trying to run her off, but you say he's OK once she is in with the flock. It's when she approaches the flock that he goes after her. That part's really confusing me.
Sometimes the flock or maybe one chicken will try to run off a chicken they consider a danger to the flock. An injured or sick chicken can attract predators which puts the entire flock at risk. That does not sound like what this is. I've had one chicken just take a strong dislike to another to the point of trying to kill them. That doesn't sound right either, he's OK once she is in the flock.
I've never had Silkies. I don't know how much the headdress might cause vision problems. This doesn't sound right either, more that I'm grasping at straws. If his vision looks like it might be obscured maybe trim a few feathers?
I don't recall ever seeing anything quite like what you describe. Part of me says as long as no blood is drawn just let it go, they will work it out. But I really don't know what is going on.