Libby

Libby was a Human female, living in the latter half of the 24th century.

Sometime in 2370, she attended a Ktarian music festival, where she met Starfleet officer Ensign Harry Kim, who had mistakenly sat in her seat. Three weeks later, Kim plucked up the courage to ask Libby out and the two began a relationship.

Libby had made such an impact on Kim that, when he became lost in the Delta Quadrant, he often woke up in the middle of the night calling her name in the hopes of a response. 

''In 2372 of an alternate timeline, Libby became engaged to Kim. The two of them lived together in San Francisco, where Kim was assigned to the Starfleet Corps of Engineers.''

In 2372, a hallucination of Libby appeared to Kim as a product of Bothan telepathy. 

Background Information
Libby, whose last name was not given, was played by Jennifer Gatti in her second of two Star Trek appearances. She only appeared in "Non Sequitur" but the character was further referenced in "Persistence of Vision" and.

Apocrypha
In the Voyager novels Homecoming and The Farther Shore, Libby resumes her relationship with Kim, although she has since become an agent for Starfleet Intelligence during his absence. The novels also state she is a musician and gives her last name as "Webber." Libby also appears in Star Trek: Voyager - Spirit Walk novels Old Wounds and Enemy of My Enemy, in which she covertly assists the senior staff when a Changeling impersonates the first officer during a mission to Loran II.

The novel Pathways gives Libby's last name as "Lattimore."