Rin is a very caring ninja who excels in medical jutsu and is extremely ahead of her time. She was on Kakashi's team while they are at war with the Stone country. She seems to have a small crush on him and she seems to be the past 'Sakura'.
Rin is also the one who did the transplant of Obito's eye and inserted it in Kakashi. This shows that her skills as a medical-nin at such a young age were extremely good. There is little known about Rin, other than the fact that she was in a team with Kakashi and Obito and the Fourth Hokage was their sensei.