I would try wood based litter. If you can't get to a pet store Morrisons (and probably most supermarkets) do a big bag for a fiver, and it's surprisingly very economical. Smells of pine, and there's none of the horrible dust that you get with standard litter. I think it's probably much better for the cats as well.
I wouldn't bother putting it in the attic tbh, I'd put it where is convenient for you. As soon as you've put it down and any time she does the circling thing, put her in it. And clean the attic as best you can... Perhaps you could get a little slide lock for it? I doubt she'd figure that out!
Just in case you don't know the best way to clean messes is with biological washing powder; it not only smells quite nice it also kills the enzyme in the poo/wee which should prevent the cat from returning * I have used a little vinegar or a couple of drop of tea tree oil in the mix to cover smells also I've noticed ppl saying put on surgical spirit afterwards though I've never tried it - I have found the bio powder to work fine by itself. xxx