It is the high concentration of nitrogen that can do it. Poop will do it too for the same reason, only slower of course, if not removed. Immediately hosing the spot down if you happen to be present should help considerably. This happens with every bitch I know. I don't think there's a lot you can do.
Bitches naturally have more ammonia in their urine than dogs, that's what burns the grass.
Changing her diet won't help. You could try asking your vet if there's anything that you can pour over that will neutralize it. I see products for this problem advertised, but do not know if they work.