Final answer:
Chrissy is utilizing the Biomechanical frame of reference to address the physical rehabilitation of Sam's fingers and wrist post-burn.
Step-by-step explanation:
Chrissy is using the Biomechanical frame of reference to guide her practice in training Sam's mom in stretching Sam's fingers and wrist. The focus on the physical aspects of movement, such as range of motion and the prevention of scar tissue formation, is central to the biomechanical approach. This frame of reference is applied to enhance function through the use of mechanical principles, such as stretching and strengthening exercises, to facilitate healing and improve physical abilities.