Now in ten hours, one can do a lot of backstitching, and I did. I stitched around the border three times - once insice the gold, and then the in- and outside of the blue - and I backstitched allll these seashells! I also stitched around her tail and fin.
Now I only have two colours of backstitching left - the rocks and her hair, mostly. There are also some special instructions, like adding blending filament, gold and beads. We'll see if another ten hours will be enough to finish her, but stitching the shells certainly was the most laborous part of backstitching!