Whatever she is she is a pretty bird...I thought of Buff Brahma in her mix too but with her comb and wattles is why I said RIR X Cochin.....Brahmas have pea combs...and every cross I have seen from them their comb is not like a reg. comb...
Can you call the lady you got her from and ask again?...
If you hadn't bought her at a tractor supply, I would have said a wheaton Marans hen. The French strain of Marans have feathers on their legs, but not as heavy as a Cochin. However, they are rare in this country so I doubt she is considering where you found her. She sure is beautiful, though!!