1.2 Gertrude and Claudius enter as the (half-new) royal couple.
1.2 Gertrude tells Hamlet to stay in Denmark and to cheer up.
2.2 When Claudius screws up Rosencrantz and Guildenstern's names, Gertrude corrects him.
2.3 Listening to Rosencrantz and Guildenstern's non-report, Gertrude tells Ophelia she hopes that the "mad with love" theory is correct – wouldn't that be nice?
3.2 The Queen watches Hamlet's play, which obviously insults her for her remarriage. Yet she keeps her cool.
3.4 Gertrude plans for Polonius to overhear her confronting Hamlet about his rude play. Instead, Hamlet gets so angry she worries he will kill her. Hamlet kills Polonius, and goes right back to calling his mother a sex-crazed immoral beast. Then he starts talking to people who aren't there (according to Gertrude and her non-ghost-seeing point of view).
4.1 When Hamlet leaves and Claudius comes in, Gertrude tells him her son is totally crazy.
4.5 The Queen at first refuses to see the insane Ophelia, but is convinced otherwise by Horatio. She tries to calm Laertes down when he storms the palace, ready for revenge.
4.7 Gertrude enters with news of Ophelia's death. It's probably a suicide, but Gertrude tries to tell Laertes in a gentle way so he won't freak out.
5.1 Gertrude strews flowers on Ophelia's grave: "Sweets to the sweet – farewell."
5.2 Gertrude drinks a goblet of poisoned wine meant for Hamlet, despite her husband's warning.