Not dispositive of self-defense. She could have felt threatened, went to the garage to get the gun, just in case, because she was fearful. If he goes after her after that, then it is still self-defense. If she goes after him, now that she has a gun, then it is no longer self-defense.
There are other elements of self-defense beyond having a reasonable fear, or a duty to retreat. One of them is that you can’t be the one to escalate to or start a deadly force fight. Going to the garage and getting the gun, instead of leaving, and coming back in to fire a shot does not make a good self-defense case.