That's a VERY common problem. Why they like it
idk, but I guess they can smell and taste the cat's food in it since cat food is really high in protein. I've had to give my cats For-Bid. It's a powder product that will make the kitty poo taste bad to the dog and it's safe for the cat. You just mix it into canned food. I haven't found a solution other than that unless there's a way you can make sure she can't get access to the litter box.