Charlie's Dad had a strong relationship with his daughter. Amongst other things, they shared an interest in restoring an old Corvette, and Charlie still isn't quite over losing him.
History
Charlie and her dad would work together on the Corvette. Her dad videotaped her diving and enthusiastically said she was a future Olympic medalist. Unfortunately soon after this, he suffered a fatal heart attack. Charlie continued to work on the Corvette, but it wasn't until after meeting the Autobot Bumblebee that she moved past her father's death.