Final answer:
Heather's problem with her height can be attributed to an issue in her pituitary gland during her growth period. The pituitary gland, which is located in the brain, is responsible for producing and releasing growth hormone, which plays a crucial role in bone growth and overall height.
Step-by-step explanation:
Heather most likely had a problem in her pituitary gland while she was growing up. The pituitary gland, often known as the "master gland," plays a pivotal role in regulating growth and development through hormones like growth hormone (GH). Since Heather is significantly shorter than average for her age but is otherwise proportioned, it indicates that she may have experienced a deficiency in growth hormone secretion or action during the critical years of growth.