I'm of the mind that your rudder is not an original Rushton rudder. I've attached a photo of a typical Rushton wood rudder. Notice that the shape of both the rudder and the rudder head are distinct and quite refined. This one happens to be curly maple, but most I've seen are cherry.
Rushton would have mounted pintles on the rudder, whereas yours has gudgeons. Rushton gudgeons would have "closed eyes" (for lack of a better term), whereas yours are open, see the top views in the second image Kathy posted.
I've never had the opportunity to see an Indian Girl set up with a Rushton rudder. Unfortunately, my reprint of the Indian Girl reprint (available from WCHA) is 200 miles away, so I can't peek in that to see what they offered, but none of the other catalogs we have access to, including 4 from the IG period 1902-1915, show a rudder designed to fit the Indian Girl. As Michael points out, the wood rudder as shown in the image is intended to go on a straight stern post. The Nomads, which are another Rushton model to be regularly fitted with rudders, have the metal drop rudders.
One last point, a couple of Indian Girl Paddler magazines from 1909 describe setting up the Indian Girl for sail, and only discuss using the paddle for steering - no mention of a rudder. It is possible Rushton, Inc., never offered a rudder specifically designed for the IG...
Cheers,
Dan