It may already be too late if you are taking her to be euthanized, you may have already done so, but on the off chance she's still with you....Have you tried the vitamin E? I'm not sure you're really looking at Marek's. I really think this is deficieny causing her troubles. In the pics you posted her comb looks pale to me and even though the feet are turned....I think you're looking at something else. Dawg53 and a few others have recommended Avian Super Pack and Rooster Booster as good high potency vitamins. A lot cheaper than euthanasia and may do the trick. Has she been wormed at all? Probably asked this before, but the answer is important. When I look at your bird, I don't see Marek's. I see a bird with possible internal parasites. This could cause a vitamin deficiency and the curled feet. It could also be something genetic as well.
With they way you feel about this girl, I would be trying everything before calling it quits. Even if it is Marek's, it's not necessarily a death sentence. I have Marek's survivors over a year old now and they are going strong. Laying every day, running, yes running, with the rest of the flock when they are free ranging. They are never going to be show quality birds....they're better than that. They have proved themselves to be survivors, against all the knocks against them. If this were me, I'd take this further, but that's me. I don't know your 'life' and all it's commitments, you do and would need to be the one making these choices. I wish you luck and peace, no matter your decisions.