She measured and cut 2 X 4’s to fit from center 2 X 4’s to the inside frame. these will be perpendicular to the center of center 2 X 4’s. This will provide more strength and something to screw boards to. Lag bolt them in from the side.
She then covered frame with more pallets
She used a specific method to cut out the arm rests which you can find at blog link below for full step by step process
She then sanded all edges to remove all sharp edges. Stained with brush, and applied polyurethane according to instructions.