Final answer:
A 6-year-old girl with juvenile idiopathic arthritis (JIA) is most likely to develop uveitis, an inflammation of the middle layer of the eye, which requires monitoring and prompt treatment to prevent serious complications.
Step-by-step explanation:
The eye condition most likely to develop in a 6-year-old girl who is newly diagnosed with juvenile idiopathic arthritis (JIA) is uveitis. Uveitis is an inflammation of the middle layer of the eye, which includes the iris and adjacent tissue. Children with JIA are at an increased risk of developing uveitis, and it is important to monitor for symptoms such as eye pain, redness, and vision changes, as uveitis can lead to serious complications, including vision loss, if not treated promptly.