Okay, one, your horse is beautiful! I mean, I'm partial to the first dark golden color she had going, but hey, she's still lovely. As for shiny...well, I can't offer too much advice. I don't own a horse, I've only got theoretical knowledge.
What theoretical knowledge I DO have says flax seeds will make any hair -- including yours -- shiny. Fresh-ground, preferably, though I'm not sure about the dosage. Buut...aha! Flax Seed
There we go. That explains it pretty well. Also? I read somewhere else that it protects you from radiation, flax. Hah!
As for the Gold as Sun type things...do the buckets come with labels? I can't find an ingredients list online, but maybe if you found on in person you could read it and try and find the individual ingredients? From what I've seen, it included different seaweeds -- which I think are good for the proteins in skin and hair -- and herbs and spices. Not so sure what those are, so I don't know what they do, but...if you could find it, maybe you could remake it without the ingredients she's allergic to?