Sister of Helios, in Greek myth

EOS

This rosy-fingered goddess signals the break of dawn and is often linked to the morning dew; her Roman counterpart is Aurora.

In Greek mythology, Helios is the sun god, and his sister is Eos, the goddess of the dawn. The clue directly references this family connection without any wordplay or hidden meanings—it’s a straightforward mythological fact. If you know Helios, recalling his siblings (like Selene for the moon and Eos for dawn) leads right to the answer. The name "Eos" also ties to words like "aurora," reinforcing her role as the bringer of daylight.