In 2268, Ybarra was one of four ensigns from the sciences division who accompanied Spock's team of three shuttlecraft to rescue Captain Kirk on the surface of the planet Anomaly. She later became stranded on the planet, chosen as one of six people whose memories were explored by the telepathic Arivne, along with Spock, Leonard McCoy, James Atheling, Andre Charvat and Sharon Follett. These memories included witnessing the deaths of her family in a freak flyer crash at age 10. She had survivor's guilt for 15 years afterward.
In a falsified distress signal set up by the Arivne, Ybarra was listed as a casualty from a transporter malfunction, with her body being stored in a stasis chamber along with Spock and McCoy. (TOS novel: Planet of Judgment)