Urine has a high nitrogen content. Since the female dog squats (rather than hiking a leg like the male) the urine is concentrated into a small area, causing a nitrogen overload on the grass, much like dumping a concentrated amount of liquid fertilizer in a single spot in your yard. One way to alleviate the grass burning, is to spray or pour enough water on the spot right after the dog urinates to dilute the strength by 10x or more. Actually, urine diluted at least 10X makes a good fertilizer for nitrogen loving plants.
Interesting factoids. I try to spray it down after she pees, but I don’t see every time.
Um, urine is also acidic, females apparently more so for some reason.