My daughter weighs 63 pounds and uses the Britax Pinnacle made in 2019. She sits forward facing - I am transitioning her from harness mode to high back booster mode and will physcially be restrained using the vehicle's safety belt. If she is using the seat belt, am I using the LATCH to attach the high back booster to the car, or am I supposed to let the high back booster be freestanding? Am I supposed to use the top tether if it is freestanding? I am very confused! All of the instructions in the britax manual address harness mode, but I don't see where it addresses how to secure the high back booster once it is no longer using the 5 point harness. Please help!