1.2 Regan sucks up to Lear to get a third of his kingdom. After Lear banishes Cordelia and Kent, Regan and Goneril talk worriedly about how to deal with their aging father.
2.1 Regan gets letters from both her father and Goneril about a fight at Goneril's house. To avoid having to take Lear into her own house, she shows up at Gloucester's castle and asks to stay the night.
2.2 Regan and her husband put Lear's messenger, Kent/Caius, in the stocks for fighting Oswald. When Lear shows up, Regan sweet talks him to avoid a confrontation until Goneril shows up. Then the two sisters have a full fledged fight with Lear about who's really in charge. Lear, furious, leaves the castle, and Regan suggests that they lock the doors behind him to teach him a lesson.
3.7 Regan and Cornwall accuse Gloucester of trying to save Lear and of generally operating on the side of good. They tie him up and interrogate him, and then Regan watches as Cornwall pulls out Gloucester's eyes. When a servant rebels at this horrific behavior and tries to stop them, Regan stabs him in the back, but not before the servant mortally wounds her husband.
4.5 With her husband barely dead, Regan decides she wants to marry Edmund. She tries to persuade Oswald, Goneril's servant, to tell her what's going on between her sister and the new Earl, but Oswald refuses. Regan suggests that he kill Gloucester, as there's now a price on his head.
5.1 In the middle of a pre-battle hookup with Edmund, Regan demands to know if he and Goneril have done the deed behind Albany's back. Edmund tells her she's crazy.
3.1 Post-battle, Regan tries to fight with Goneril over Edmund, but finds herself too sick to really do anything. We find out later that Goneril has poisoned her, and Regan dies offstage.