Olympias II of Epirus

Olympias (in Greek Ὀλυμπιάς, ; lived 3rd century BC) was a queen and regent of Epirus. 
She was daughter of Pyrrhus, king of Epirus and his first wife Antigone. She was the wife of her own paternal half-brother Alexander II. 
After his death she assumed the regency of the kingdom on behalf of her two sons, Pyrrhus II and Ptolemy; and in order to strengthen herself against the Aetolian League she gave before 239 BC her daughter Phthia in marriage to Demetrius II, king of Macedonia. By this alliance she secured herself in the possession of the sovereignty, which she continued to administer till her sons were grown up to manhood, when she resigned it into the hands of Pyrrhus II. But the deaths of that prince and his brother Ptolemy followed in quick succession, and Olympias herself died of grief for her double loss. Such is Justin's statement: according to another account Olympias had poisoned a Leucadian damsel named Tigris, to whom her son Pyrrhus was attached, and was herself poisoned by him in revenge.