Here's the 43.5" long Rachel Roy Fold Waist Dress. As far as I can tell from the pictures, it seems to fit every rule of tznuit.
It's currently $240 + tax at Neiman Marcus, which is just over 50% off its retail price of $500. Only sizes 4 and 8 remain there. Alternatively, it's currently available for $300 on Rachel Roy's website in sizes 0 and 16. It appears Nordstrom used to sell it, but they're out of stock.