This event is situated in Southsun Cove. Holding the four settlements (Point Pride, Kiel’s Outpost, Steampipe Steading, and Camp Karka) will cause the Crazed Karka Queen to appear.
You need to throw Karka eggs on the ground at her to break down her defenses. Players will have 10 minutes to defeat her. Defeating her will grant you a daily chest (account bound) containing two rares. There is also another chest you can loot that grant you 2 items. The Karka Queen have a cooldown timer so she won’t always spawn when all four settlements are under control. (Cooldown timer seems to be about 1 hr).