what evidence is there in this scene that hamlet's advice has an effect on gertrude?

I think we see here that Gertrude truly didn't know about the fact that Claudius had killed her late husband. Despite the fact that Hamlet has killed Polonius, she says there is a morality in her son,

"O'er whom his very madness, like some ore

Among a mineral of metals base,

Shows itself pure. He weeps for what is done."