You're conflating what led up to the shooting with what justified it. I don't think you've demonstrated that lethal force was necessary in the first place.
"She was accelerating toward him" doesn't settle that, especially since Ross had moved to the side of the vehicle when he fired. And "he got bumped then he fired" is your assumption. There's no established proof that the vehicle actually made contact with him. Even granting your interpretation of the skid and the preceding events, that doesn't establish that Ross faced an imminent deadly threat when he pulled the trigger. At most, it explains why the situation escalated.
So the shooting looks less like demonstrated necessity and more like an impulsive act of vindication or hostility. I'm not claiming to know his exact motive, but you can't simply assume necessity either.
As for immigration, human migration is a normal behavior, while immigration restrictions are political systems imposed upon it. I don't think immigration status is a sufficient justification for expanding coercive state power over ordinary people. That's why opposition to illegal immigration doesn't make the use of disproportionate force legitimate, nor does it make the immigration issue relevant to whether this particular shooting was justified.
You also keep invoking what illegal immigration supposedly does to a country without acknowledging that the overwhelming majority of crime isn't committed by immigrants in the first place. Crime, violence, and social dysfunction existed long before the current immigration debate and are largely produced within the non-immigrant population as well.
There's also a broader issue of selective enforcement. Some crimes and abuses get minimized or ignored when the people committing them occupy a politically or culturally favored position, while immigration status can make someone a convenient target for disproportionate scrutiny. So I don't see "illegal immigration causes problems" as the self-evident justification for expanding state coercion that you seem to treat it as.