Susan Delgado appears in Wizard and Glass, the fourth book of the series. She is a resident of Hambry in the Barony of Mejis, where the 14-year-old Roland and his ka-tet have been sent for safekeeping. Her father was killed in a horseback riding "accident", actually a murder, and Susan has been cajoled by her aunt Cordelia into becoming a "gilly", essentially a concubine, for Mejis mayor Hart Thorin (while Susan is paid for her services, she is a recognized consort and any heir she bears to the heretofore-childless Thorin will be legitimate). Before her relationship with the mayor is allowed to begin, however, she falls in love with Roland, and lays plans to run away with him. She saves Roland's group from imprisonment and possible execution. Accused of helping the gunslingers kill the mayor, she is burned at the stake by the townspeople and her aunt. At the time, she is already pregnant with Roland's first child. Roland is devastated by her death—not just because of his love for her, but because, when confronted with the choice of returning for her or setting out for the Dark Tower and thus saving all of creation, he chose the Tower, thus condemning her to death.

Roland believes that Susan Delgado was the only true love of his life.