Eve is the young daughter of Lord Dalgorel, the ruler of Terrabelle, and one of the Fair Folk. She is a precocious young girl with a yearning for adventure and new experiences, and greatly exasperated by her people's indifferent ways and being confined to Terrabelle.
In Wrath of the Dragon King, she finally gets her wish to see Dragons when she accompanies her father to the Feast of Welcome, hosted by Celebrant in his castle at Skyhold. She got to attend because her father needed a companion and her mother doesn't like journeys. Upon meeting Kendra and Seth again, Seth surprised everyone by kissing Eve's hand (presumably because he was under the influence of a courage potion to counteract Dragon fear).
After the Feast of Welcome concluded, rather than return with her father to Terrabelle, Eve snuck away and followed Kendra, Seth, Tanu, and Calvin on the High Road on their journey back to Blackwell Keep.
She helps them using her magical talent that allows her to conceal herself and those around her from unwanted scrutiny. The longer she uses her gift, the quicker fatigued, especially if she uses it to hide more than just herself. She says her gift works best when things she disguises are only half noticed.