She'd taken 14 days to cross the Atlantic on a carbon-neutral journey via boat for climate change summits in the US and Chile.
But at the last minute political unrest meant the Chile talks moved to Spain.
She needed a crew to take her back to Europe - and she needed them quickly.
That's when Nikki Henderson stepped in.
"I helped because I wanted to see what Greta was really like, get to know her and be able to educate myself about what she represents," the 26-year-old British sailor tells Radio 1 Newsbeat.
The problem was that Nikki was ...
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