Sudden Summer by Gilda Harrington

Sudden Summer is the story of Rosie Malone from Bigstone, a small town three miles from nowhere, who learns that her best friend Dawn is a lesbian. When Rosie joins Dawn (and 4000 others) at the women's music festival, she discovers that she, too, is gay. Bewitched by Calypso, a strangely sensuous singer, she begins to wonder if she can ever make it home again. And with whom.