So the reluctant flier traveled to the jungle-covered mountains of Costa Rica, thousands of miles away from her home in England's leafy countryside, for a psychedelic retreat.
In the space of two weeks, she ingested a flood dose of Iboga, a tree bark used to induce visions; took Kambo, the poisonous secretion of a giant tree frog hailed for its healing powers; and had experiences with ayahuasca, a hallucinogenic brew. All have been used in indigenous cultures for centuries as part of Shamanic spiritual rituals.
Bradbrook recalls being terrified but determined to push herself to the limit and divine a greater sense of purpose. During an ayahuasca ceremony one evening, she offered up a prayer calling on the universe to show her the "codes for social change."
Two years later, Extinction Rebellion was born.
'This was my prayer being answered'
Bradbrook, one of the founders of the world's most high-profile environmental movements, felt as though the trip had rewired her brain. "It was utterly transformative," she told CNN in a recent interview at her home in the English town of Stroud.
After Bradbrook returned, she ended her marriage and began to work with a group of activists, including Roger Hallam, a Welsh organic farmer pursuing a PhD at King's College London in radical campaign design.
When their first lengthy meeting wrapped, Hallam turned to Bradbrook and said, unprompted, that he had just given her the "codes" she had been searching for. His words sent a chill down her spine.
"It's an Extinction Rebellion mythic story that's out there, but it's true," said Bradbrook, who has a PhD in molecular biophysics herself. "I was very gobsmacked and at the time I remember thinking, 'goodness me, if he hadn't used that phrase, I wouldn't have recognized that this was my prayer being answered.'"