Electra
Electra was the second daughter of Agamemnon and Clytemnestra. After her older sister Iphigenia was offered for sacrifice and her father departed for the Trojan War, her cousin (first cousin once removed and second cousin) Aegisthus moved in with her mother. Seeing which way the wind was blowing, Electra arranged to smuggle her little brother Orestes out of the kingdom so he could grow up in relative safety.
Upon his return from the Trojan War, Agamemnon was murdered by his faithless wife and her lover. They then arranged a marriage between Electra and a peasant, figuring that the children of a peasant would be less likely to try to avenge the murder of their grandfather than the children of a noble. The peasant, however, refrained from consummating the marriage, and it was later annulled.
When Orestes returned as a grown man, accompanied by his loyal ally, Pylades, and under orders from Apollo to avenge his father's murder, Electra assisted with the arrangements but did not herself strike Clytemnestra, so she was not tormented by the Furies as Orestes was. After Orestes' guilt for matricide was expiated, he and Pylades returned and Electra married Pylades. The curse of the House of Atreus having finally been lifted, Electra apparently lived out her life in relative peace.