Tonia Barrows was a female Human who was a member of Starfleet in the 23rd century.
In the 2260s, she was assigned to the USS Enterprise. She and Dr. Leonard McCoy flirted while on the Amusement Park planet, and later began a relationship. (TOS episode: "Shore Leave")
Not long prior to the incident with the Guardian of Forever in 2267, Barrows was promoted to the rank of ensign and received a transfer from the position of Yeoman to physical sciences division of the Enterprise. However, she then transferred to the USS Godel, upon which she served for almost three years. (TOS - Crucible novel: Provenance of Shadows)
She was then promoted to lieutenant and assigned to the USS Defiant. However, she was injured, and left the Defiant. (TOS comic: "A Small Matter of Faith")
In 2281, Barrows was a Commander assigned as the commanding officer of the Early Warning Monitoring Station at Jupiter Station, a position she still held in 2283. (TOS novel: Elusive Salvation)
It is revealed that Barrows and McCoy resumed their romance, eventually marrying after 2293. (TOS - Crucible novel: Provenance of Shadows)