Yill'uop was part of a group of travelers on the planet Talus. When a storm hit the group's area northeast of Dearic, Trenrel found a cave where the group sought shelter. The group decided to investigate further into the cave and set up camp deep in the vast cavern. During their second day in the cave, the group was attacked by giant fynocks and Yill'uop was killed by one of the flying creatures as she turned to run.
Sources
10 Hot Spots Travel Guide on the official Star Wars Galaxies website (content now obsolete; backup link)