A teenager who wanted a world without borders for the people the Blip had displaced, and took a serum and a bomb to get it.
Karli Morgenthau is the teenage leader of the Flag Smashers, an anti-nationalist group Wikipedia describes as terrorist, made into super soldiers with the help of the Power Broker and using violent tactics, bombings among them, to achieve open borders for refugees in the Baltic states. Erin Kellyman plays her in The Falcon and the Winter Soldier. The reader who sent this list described her as a young girl who wanted to make sure there were no more borders for the world, which is how she would put it herself.
Minor spoiler
The Power Broker is Sharon Carter. Karli is killed by her, to hide that identity, after Karli tries to kill Carter and an oblivious Sam Wilson.