Hello, I understand your frustration with this problem and it is a common one.
It is related to the increased amounts of nitrogen and the pH of her urine, both will burn the tender grass blades. Females tend to cause more of a problem as they empty their bladder in one or two spots so there is a large amount of urine in one area unlike males that go on several spots thus the amount on each area is less.
There are all sorts of products out there that purport to help but as I'm sure you've seen with the rocks they do not work. Most of the time they work by trying to change her urine pH, which is only half the problem, and which can be dangerous for her, causing her to form urine crystals and possibly urinary tract calculi. The only thing that can be done safely to her is to increase the amount of fluids she takes in as the more dilute her urine is the less it will burn. Increase fluids by feeding more canned food, adding water or low salt broth to her food, and giving her ice cubes to lick and play with.
You have a couple options. One is to try to train her to urinate in only one part of the yard where you place artificial turf or pea gravel. Or you can choose to go with her when she goes outdoors and thoroughly water the area she urinates on to dilute the urine.
I'm sorry that there isn't a better solution out there, but I don't want you to waste your money on products that don't work or would harm your dog.
Please let me know if you have any further questions.