Sarjenka was an inhabitant of Drema IV.
She had been communicating with Lieutenant Commander Data through an RF transmitter for eight weeks in 2365. He became aware that her planet was tearing itself apart due to geological shifts caused by an unusually high concentration of dilithium lattices in the planet's crust. Initially, Captain Picard ordered Data to cease contact with Sarjenka to prevent any further violations of the Prime Directive. However, Data urged intervention and the captain eventually allowed the crew of the USS Enterprise-D to stop the geological shifts by destroying the crystals with modified probes. To lessen the contamination that the crew of the Enterprise-D had caused, Picard ordered Doctor Pulaski to erase Sarjenka's short-term memory. But in the process of returning her to Derma IV Data left her with the Elanin singer stone she saw in sickbay so that she could keep a small part of her experience with her. (TNG: "Pen Pals")
In the non-canon Corps of Engineers eBook series, Drema IV was invaded by a species known as the Exiles, and then became a Federation protectorate after they cast out the invaders. The now-grown Sarjenka became the first Dreman in Starfleet, enrolling in Starfleet Medical Academy, and eventually becoming deputy chief medical officer of the U.S.S. da Vinci, eventually regaining her memory of the events of "Pen Pals."