Cadet Gaila is a red-headed Orion woman, who is Cadet Uhura's roommate. Thus we can conclude that she is in Kirk's, Uhura's, and McCoy's graduating class. In the film, she tells Jim Kirk "I think I love you," right before Uhura walks in on their make-out session. The movie doesn't indicate whether or not Gaila is assigned to the Enterprise and therefore survives the battle of Vulcan. It seems unlikely she would not be a repeat character, however, and she may appear in future films.
Orions are green-skinned humanoids, and Orion women have appeared throughout Star Trek as "slave girls," i.e. concubines. Although in Enterprise (TV Series), it is suggested that Orion society is matriarchal. The slavery aspect of the society does not subdue the women, but rather enables them to move about "freely" by commanding their masters to sell the women to whom the women wish.
Orion women are known for sexual prowess and appetites that are beyond the capacities of other species. Naturally, the character of the womanizing Kirk would gravitate towards her hypersexuality. This makes for a potentially super charged relationship that is, well, characteristically Kirk. Gaila, although 'civilized' Federation citizen seems to still live an active sex life. Gaila: "My roommate [Uhura] asked me to stop bringing men back to the room." Kirk: "How many have you brought back here?"
It should be noted that Cadet Gaila is not a slave -- the Federation has outlawed slavery. Joining Starfleet is counter to the Orion culture, which can be summarized as a pirate culture. There is certainly an interesting, unknown character story to be told. Perhaps she was adopted by Federation parents.
