Has Gertrude reformed after her confrontation with Hamlet in Act 3, Scene 4?
My answer would be no, but a complex no. By that I mean, I don't think Gertrude knew about what Claudius did to her husband. She doesn't seem that guilty, or in the know, or, to be frank, like a conspirator. I think that she might have some suspicions or fears, but they are distant, and that's all they are. That scene, then, can't reform her because she's not actively evil/guilty at that time. What it does is rupture her distance from things, so that after that she's more emotionally involved. She seems to feel responsible for Polonius' death, and perhaps for her husband's, and for Ophelia's madness.