She drank poison.
Aids.
Gertrude, Hamlets mother.
Hamlet is talking to the Ghost, which Gertrude can't see, which looks bizarre to her. For the first time, Gertrude sees Hamlet as seriously mentally ill, not just disturbed. Ironically, it's Gertrude whose perceptions are faulty in this scene.
Hamlet kills Claudius by stabbing him with the poisoned sword Laertes carried and by forcing Claudius to drink the dregs of the poisoned drink which killed Gertrude.
Polonius is listening to Lord Hamlet's meeting with Gertrude behind the curtain.
Gertrude Aretz died in 1938.
Gertrude Morgan died in 1980.
Gertrude Appleyard died in 1917.
Gertrude Bloede died in 1905.
Gertrude Cosgrove died in 1962.
Gertrude Johnson died in 1973.
Gertrude Elles died in 1960.
Gertrude Melville died in 1959.
Gertrude Neumark died in 2010.
Gertrude Hartland died in 1954.
Gertrude Hullett died in 1956.
Gertrude of Sulzbach died in 1146.