I bought a Diono car seat intending to get 10 years use for our daughter. At 7 years old and 128cm tall, I swapped out the harness for the sestbelt. Using the seatbelt guider the belt comes over her arm and not over her shoulder. The headrest is at maximum height. How do I make this safe for her? It looks like she has outgrown it but she is well below the maximums for the seat.