I can't sleep....here is the other picture you found on ebay...
Now we need to find the original and the copyright holder. Sleuth on!
I know I have seen this picture before...possibly in a child's Texas history textbook or some other common source like that...I almost think the girls(s)? are in separate photographs or paintings in their original context and Ward has possibly spliced the two girls into one "work"...But the person on the left definitely looks familiar to me.
It would be fairly easy to sent the cropped and enlarged grouping to a few of the many Indian historians on the web, asking them if the people look familiar, without telling them why you want to know. It might even help to see it in black and white, most likely its original form:
There are a lot of old Indian photos, but there number is finite...and there are not so many of them that someone, somewhere hasn't seen them before...in a museum, a textbook, or elsewhere.