From your description, I suspect you're using one of those litter trays with sides that are only a couple of inches high. (Otherwise it would be difficult for her drag litter out while being outside the box.) I would use those only for kittens, or for a cat that is injured or ill. If that's what you're using, I recommend you get a litter box where the sides are more like 6-9" tall. It doesn't have to be one of those fancy covered litter boxes -- in fact I prefer not to have it covered so that I'll see immediately if it needs scooping. But it should have enough room so that your cat can use one end for peeing and the other end for pooping, while the middle part that she stands on stays clean. I often use rectangular tubs from the hardware store.
Make sure the litter box is in a low-traffic place. Your cat may decide to use both ends of the box for peeing and pooping, but many of my cats have preferred to "specialise". The high sides of the box will make it difficult for her to stand outside the box and scoop litter, and it will also add to her feeling of privacy. She may stand outside the box and scrape at the sides. This is common in cats. I think it's sort of an "I need to cover my waste" instinct on overdrive, but it doesn't do any harm.
In general, litter box behaviour problems generally occur because the box isn't big enough, private enough, clean enough, or the cat finds the litter uncomfortable to stand on.
EDIT: OK, I see from your picture that my first theory was wrong, and that your cat is very determined. I have a couple more suggestions:
- Remove the cover temporarily, and see if she still does it. I don't expect this to help, but it's easy to do and worth a try.
- Try a bigger box (the width is fine, but try something much longer). I hate to suggest this because that looks like a very brand-new nice box that most cats would be quite happy with, but if you get desperate enough, this is worth a try. I don't think you'll be able to find a covered litter box as big as I'm suggesting, but you can find a suitable plastic tub at the hardware store. I suspect that she is peeing or pooping right inside the door, and doesn't feel like she has enough room to stretch her paws forward to scoop the litter behind her.
Perhaps someone else will have a another suggestion that you can try first.