She’s referring to rebellion. And the Solo novelization by Mur Lafferty, out on September 4, added an epilogue showing exactly who Enfys gives the coaxium to: Saw Gerrera, who’s accompanied by a young Jyn Erso.
Given that Two Tubes, a member of Gerrera’s partisans in Rogue One, was part of Enfys’ gang, this hand-off isn’t the most surprising thing in the world. Saw was there at the beginning of the insurgency, and though he didn’t join the Rebel Alliance because of his extremist ways, he fought back against the Empire–I can’t help but wonder how often he and Enfys crossed each other’s path. Her comments to Han, her actions, and this hand-off cement Enfys as an important player, and I want to know more about how she fits into the bigger picture.
Since Jyn is with Saw, this meeting takes place after the beginning of Rogue One and during the novel Rebel Rising. Jyn’s young, and Enfys, a teenager, shares important advice with Jyn: “Still, they’re going to underestimate you [because of your age]. Make them regret it.” It’s easy to see Jyn channeling that as she rallied the group of rebels that would bring hope the galaxy.