From the Sarasota Herald Tribune:
[Vickie] Rock, 50, of Riverview, came outside armed with a .45-caliber handgun and saw [Daniel] Robertson beating [his girlfriend Christy] Vasilakos with a metal object, said Hillsborough sheriff’s spokesman Larry McKinnon.
When Rock tried to intercede, Robertson turned on her. Rock suffered several facial injuries before firing at least one round and striking Robertson, McKinnon said.
The rest of the story provides some more details, including Vasilakos’s perspective on Robertson (though of course one should take any media accounts in such a situation with a grain of salt, and more broadly take everyone’s accounts with a grain of salt). From the story, Rock’s actions seem perfectly legally proper — and likely would be seen as legally proper even in duty-to-retreat states — and morally praiseworthy.
At the same time, though much depends on the nature of the metal object, it seems likely (though not certain) that if Rock hadn’t intervened, both Robertson and Vasilakos would be alive today. Indeed, it seems possible (though far from certain, and perhaps not knowable to us) that Rock might have thought that she could have saved her own life, at the expense of submitting to the beating, even without shooting Robertson.
So whether you think this was a laudable instance of self-defense (as I do) or something that you think shouldn’t have happened may turn not just on whether it’s good to take an attacker’s life to save the victim’s life, but also whether it’s good to take an attacker’s life to prevent likely harm that is likely to be well short of death. The law in all states says yes, in allowing killing not just to protect life but also to prevent serious bodily injury (including rape), and also, in many states, to prevent robbery or even many kinds of burglary. I think that’s also morally right, at least as to serious bodily injury and rape, and likely as to other serious crimes as well. But the issue strikes me as interesting, precisely it’s (at least sometimes) not just “it was his life or mine.”
UPDATE: Just to make clear, there are two legal defenses in play here — Rock was justified in threatening Robertson by the “defense of others” defense, and then justified in killing Robertson by the self-defense defense, given that Robertson had turned his attention to her.