Just for some context at the end of Chapter 15, Frenchie shoots Travis.
French sees one of RiRi's pink boots on the edge of the cliff. That empty boot makes French understand what happened. He rushes back to camp. Travis correctly guesses that Lincoln killed RiRi, and curses him for continuing to use drugs. Travis offers to help French and the others escape “the white boys,” and Tree points out that Travis is tied up and cannot go anywhere. French shoots him, killing him immediately. I think this is a reflection of Frenchie's frustration. In reality, killing anyone does not bring Riri back but Frenchie's rage is understandable.
