You need to immediately take your friend to a paediatirc rheumatologist (doctors specialising in
arthritis of children). In Delhi, Dr. Sujata Sawhney is available at 98114-44116. In Chandigarh, at the Postgraduate Institute there is Dr. Surjit Singh (unfortunately I do not have his number with me). Dr. Amita Agarwal is at Sanjay Gandhi PG Institute in Lucknow and Prof. C. Rajendran is in Depart of Rheumatology, Madras Medical College and Govt. General Hospital.
I must also convey to you that most serious forms of arthritis (including rheumatoid arthritis) are
autoimmune in nature where immunity starts hitting ones own body and this group of diseases occur much more often in girls/women and usually in the 2nd to 4th decade of life with peak age between 15 years to 35 years. Therefore, for experts it would not be a surprise at all that a 12 year girl has arthritis. This category of arthritis is called Juvenile Idiopathic Arthritis; its old name was juvenile rheumatoid arthritis.
A good news is that if the diagnosis is confirmed, there are wonderful new medicines that would make your friend better very soon although she may have to continue medicines for several years.
Finally, I must plead that please do not waste time in alternative systems of medicines because time is of essence. If diagnosed and treated very early in its course, permanent damage would not occur. Go for modern scientific medicines only and go only to specialists because average doctors have no clue about this disease. I hope I made my point. Good luck.