By all means I think if a stranger breaks into your house you should be able to shoot them, because you have no idea if they are armed and by the time you find out it may be too late.
OTOH Someone that a person knows is a poor test of this law, because it is too hard to tell. For example maybe the man was a threat, or maybe he was there to tell her he was leaving her for someone else and she shot him? More details need to be known.
That's the problem with situations like this. Perhaps she was defending herself against violent assault. Then again, perhaps she decided to lure him over for whatever reason, shot him, and then banged her arm against some furniture to make some good-looking bruises. It can be too easy to make premeditated murder look like self-defense.
That said, shooting some stranger busting into your house should be open-and-shut self-defense, especially if the shot person had prior offenses.