The Sacred Well by Antoinette May

In another century, another writer is fascinated by Alma's tragic story. Drawn restlessly to Yucatán—and away from the stifling needs of her desperately ill partner—Sage Sanborn is tempted by her growing feelings for David, a scientist who encourages her to delve deeper into Alma's history. And in this ancient place of mystery and spirits, Sage must make an impossible decision that will forever change the course of her life.