So, you are right, justified shootings are under reported. However, regardless, that has no effect on the relevant metric: firearm homicide rate.
Interesting that you guys keep running from the truth; it is the available number of guns, like this one - floating around and getting into the wrong hands that causes gun violence to go up. Guns are quite inanimate in themselves, but when a two year old picks one up and shoots himself, that gun becomes the problem that we're talking about. That same problem, of an errant firearm, is exactly why that woman is dead.
You can dance without a lawyer
Believing that Guns are the Cause of Murder is like believing that Pencils are the cause of Misspelled Words.