Caithlin was aware of her Human ancestry, but spent her entire life trying to make amends for it. The moment she reached the allowed age, she applied for the diplomatic service. Dar was worried that she would be turned down, and even threatened legal action if she was denied due to her grandfather being a Human. Luckily for her and the service, she was more than qualified and was accepted. Caithlin knew that she would not get any plum assignments, so she volunteered for the worst assignment she could find. This turned out to be Nimbus III.
Dar was trilingual, having mastered Federation English, a small amount of Klingonese and her own native Rihannsu. Her grandfather was from Ireland on Earth, but Dar was raised by her mother on Romulus. Dar's colleague, St. John Talbot, who hailed from England, took note of this fact.
Just after arriving on Nimbus III Dar, Talbot and Korrd were taken hostage after Paradise City was besieged by Sybok's Galactic Army of Light. After being persuaded to abandon her past resentment of her mixed background, Dar helped Sybok and his forces overpower Captain James T. Kirk and the Starfleet Security team sent to rescue her. Later, Dar, along with the other two diplomats, went on a pilgrimage to Vorta Vor aboard USS Enterprise-A. (TOS novelization: Star Trek V: The Final Frontier, TOS comic: "Star Trek V: The Final Frontier")
When Dar introduced herself to St. John Talbot, he said he had never met a Romulan with an Irish first name. Dar replied that she had never met a living saint. (TOS novelization: Star Trek V: The Final Frontier)
In an alternate timeline created by Spock's death in 2237, Dar was also the representative to Nimbus III, but had become friends with Saavik (who had become a diplomat instead of a scientist) prior to 2285 and assisted Thelin th'Valrass in rescuing her. (TOS - Myriad Universes novel: The Chimes at Midnight)