A close-up of Anna's necklace
Anna was a persona assumed by Voval, an Iyaaran ambassador, based on the logs of Anna, a Human female who had survived the crash landing of the Terellian cargo freighter. The persona was created as part of the Iyaarians desire to study Human emotions, as they had no natural understanding or social forum for concepts such as love, antagonism, or pleasure.
As part of a concerted effort with Iyaaran ambassadors Loquel and Byleth to study these emotions, Voval posed as a shuttle pilot sent to transport Captain Jean-Luc Picard to Iyar as part of a cultural exchange program.
After staging a crash landing on a class M planet, Voval assumed the role of Anna, who claimed to be the sole survivor of a Terellian cargo freighter that had crashed seven years earlier. Anna informed Picard that he had suffered three broken ribs and that Voval had perished in the crash. When asked to remove a comm panel from the shuttlecraft in order to send a distress signal, she claimed to have inadvertently destroyed the transmitter module while removing it. Anna then surprised Picard by kissing him, and telling him that she loved him.
After discovering that his ribs were not, in fact, broken, Picard confronted Anna, whom he now suspected was keeping him captive. Distraught by Picard's analysis of the situation, Anna ran out of the room while tearing off her necklace. After he was imprisoned inside the crashed cargo ship, Picard discovered Voval instead, who quickly attempted to explain his apparent fatality; an Iyaaran's metabolic rate slows down to promote healing when injured, giving the appearance of death. The two split up, going off in search of the elusive Anna.
Picard discovered her at the edge of a cliff, where she threatened to commit suicide if he wouldn't profess love for her. Noticing that Voval was nowhere in sight, and that her necklace had suddenly returned to her neck, Picard encouraged her to jump. At this moment, Voval withdrew his disguise and revealed his true intentions. Using Picard as a subject, he had set out to study the emotion of love, the nature of which he believed he had failed to learn. (TNG: "Liaisons")