Would one year of steroids for JRA during teen years (with subsequently well-controlled autoimmune disease) be sufficient to explain a vertebral T score of -4.4 of a woman in her early 50s without any other risk factors?  

This is a tough question. It is clear that teenage years with GCs would impact peak bone mass, however not to this extent. A T score of -4.4 is the result of a low peak bone mass, genetics, and factors that affect the bone mass between ages 25 to 30. I would put forth part of the low BMD is from GC ...