Enya Geil is one of Dio's most loyal supporters, and the one who originally gave him the Stand Arrow, which she obtained from Diavolo. She is the mother of J. Geil. Her stand is Justice, which is able to control people through their wounds, whether alive or dead.
For legal reasons, her name is changed in the American version of both the game and the manga, to N-Yah Gail and Enyaba Geil respectively.
In the OVA:
She is able to change her appearance from that of a young woman to an old lady at will. No explanation as to why is ever given.