Nemesis was a Greek goddess, so her family tree would be the family tree of the Greek gods. Some accounts say she was the daughter of Zeus, but Hesiod describes her as the daughter of Erebus and Nyx.
Nemesis is the goddess of divine retribution and revenge. She punished those guilty of hubris. In the earliest Greek religion, Nemesis was worshipped as a fertility goddess. Legend said that while Zeus was in the form of a swan and she was in the form of a goose, they copulated. The result of that union was an egg. That egg hatched a baby who became Helen of Troy. Later versions of the legend claimed that Leda was the mother of Helen.
Today the word nemesis is used in the English language to describe an arch-enemy. It is an opponent or rival that cannot be overcome.