Another Rousseau explanation we need to see: she was around for the final four years of the Dharma Initiative. She was there for the Purge when the entire Island was gassed with poison gas. How did she survive? Did the gas only get dispersed at Dharma locations, so she was safe out in the jungle? Because the implication we've gotten is that the gas reaches EVERYWHERE on the Island, hence the threat of Faraday having to disable it in "Other Woman".