The Waterfall, by Marion Zimmer Bradley

A young woman finds her psi talent, and it's evil.

Also, it's worth mentioning that the young girl, Sybil, is "fifteen years old and as frail as a branch of willow," which is disturbing considering that author Marion Zimmer Bradley describes her using sex to entice and ultimately murder someone, and also considering the claims of child sexual abuse made against Marion Zimmer Bradley by her own daughter. One suspects Bradley may not have fully understood the enormity of what she wrote in The Waterfall.

Bradley escaped justice in this world, but there is a day of judgement in the life that is to come.