Paprika is *supposed* to help with black coats, but I have no personal experience and that's all just hearsay. Google it for feeding instructions.
I don't know what sort of feed you've got her on, but I'd say she needs some sort of protein. The corn oil is a good idea already. It's that topline where she's really lacking, and in addition to a good feed program, she needs to be ridden properly (and well-padded to prevent soreness). Lots of suppling, hill work, trying to work in frame (but allowing her time to relax and stretch, too, since she is so out of shape).
A few tack points I couldn't help from notice from the pictures, though:
In the 'before,' the curb chain is on the wrong part of the bit--it should be on the top ring where the bridle attaches. In the 'now,' the halter underneath the noseband is causing the muzzle ring to dig into her nose, which is probably uncomfortable. Just didn't want you getting hurt from equipment malfunctions...