A Jest of God by Margaret Laurence

Republished as 'Rachel, Rachel'. A shy, unmarried schoolteacher named Rachel Cameron experiences a summer of self-discovery and emotional awakening in rural Connecticut. While her repressed emotions are initially triggered by a visit from a preacher and a religious experience, it's her lesbian best friend, Calla, who offers both support and a tentative overture of lesbian love. Rachel, initially repulsed by Calla's advances, realizes the importance of embracing life and ultimately engages in a sexual encounter with a childhood friend, Nick Kazlik.