Who is Sybil in Greek mythology?

Sibyl is most likely a title, indicating a oracular women believed to possess prophetic powers in ancient Greece. The earliest Sibyls, prophesied at certain holy sites, under the divine influence of a deity.

In Greek mythology, Sibylla is so told to be :

Pausanias, Description of Greece 10. 12. 2 (trans. Jones) (Greek travelogue C2nd A.D.) :

"There is a rock rising up above the ground [at Delphoi]. On it, say the Delphians, there stood and chanted the oracles a woman, by name Herophile and surnamed Sibylla. The former Sibylla I find was as ancient as any; the Greeks say that she was a daughter of Zeus by Lamia, daughter of Poseidon, that she was the first woman to chant oracles, and that the name Sibylla was given her by the Libyans."