Erato was the daughter of Polyxo and Danaus. She took part in the mass marriage of the fifty daughters of King Danaus to the fifty sons of King Aigyptos. She would wed Bromius. That night she and forty-eight of the other forty-nine daughters killed their respective husbands with daggers provided to them by Danaus.
When Erato and the other Danaids who had murdered their husbands they were sent to Tartarus and were forced to carry water from the river Styx in a bowls (or jars according to some) with holes over to a tub which leaks at multiple parts. Erato and the others were told only when they filled the tub could they wash away their sins. The Danaids continue this essentially impossible task to this very day.
King Danaus & Polyxo
"The twelve sons of a Naias Nymphe named Caliadne [and Aigyptos] drew lots for the daughters of Polyxo, also a Naias [and Danaus]. The sons were named Eurylochos, Phantes, Peristhenes, Hermos, Dryas, Potamon, Cisseus, Lixos, Imbros, Bromios, Polyctor, and Chthonios; the girls were Autonoe, Theano, Electra, Cleopatra, Eurydice, Glaucippe, Antheleia, Cleodore, Euippe, Erato, Stygne, and Bryke."
- Apollodorus, Library 2.1.5