cthattcher,
She should see a hand surgeon.
She does not have pain, because she is not using or bending the finger. There are several causes of an extended finger. But, this other joints in the hand being swollen, she may have an arthropathy of some type. However, since the pain is going up the forearm, it could be a tendon problem, as the muscles that bend the fingers are actually in the forearm, with their tendons running distally all the way to the fingers. So, a tendon problem can cause discomfort from the tip of the fingers to the elbow. inflammatory flexor tenosynovitis is a common disorder of the fingers. Often, patients will hold the finger in an extended position, because it hurts to flex it and sometimes the tendons will get stuck in the flexed position. So, the patient does not move the finger, and after a while, the finger becomes stiff and it is no longer possible to move the finger. But, again, there are a multitude of reasons for a finger not moving.
A hand surgeon can diagnosis hand disorders and can treat most problems. So, if you are going to pick just one physician, go with the hand surgeon.
Hope your aunt is feeling better soon. Good luck.