Origin

Gem was given her name by Leonard McCoy. He gave her this name because her race has no vocal chords and he needed to call her something so he came up with Gem.  Gem is an empath.  She has the ability to heal someone's wounds by taking it herself.  The wounds literally transfer from the wounded person's body to her own body and then they become healed.  The whole process takes a couple of minutes.
 
When McCoy, James Kirk and Spock met Gem they were being held prisoner and tortured by two Vians named Lal and Thann.  The torturing went on and Gem would heal them but was afraid to heal someone who was near or at death because she could die herself.  In the end she risks her life and the Vians let the crewman go having accomplished there goal of pushing Gem to that point.

Creation

Gem was created for the Star Trek television show.