Is it possible for a teenage girl to have chronic back pain? if so, why?

Yes: From a podiatrist's perspective, flatfeet can be a cause of chronic back pain, even in a teenager. A big chest can be another source of back pain in a teenager that i can think of.

Yes. Many reasons.: Chronic back pain is defined as pain lasting longer than 6 weeks, so it is certainly possible for a teen to have chronic back pain. Possible causes included strain, trauma, poor posture, poor body mechanics, over-activity in certain sports, body habitus (size, proportion, etc.), and even congenital (deformity at birth). Best to see your doctor to better identify your specific cause.