Terrie is involved in the quest Act of Mercy.
Ser Thrask sends Hawke a letter asking them to come to a remote cave on the Wounded Coast. When Hawke arrives, Thrask reveals that a group of apostate mages who escaped from Starkhaven are hiding inside. Hawke must convince them to surrender or else Thrask's comrade, Ser Karras will arrive and likely slaughter them. The group is lead by a Blood Mage named Decimus. Several of the apostates assist Decimus while the other Apostates, including Grace and Terrie refuse.
After killing Decimus, Hawke can convince the survivors to flee. Terrie is one of the mages who escapes and evades capture. She later contacts Hawke through Mistress Selby, thanking Hawke for her freedom and offering other opportunities to aid mages.Alternatively if Hawke turns the mages over to the Circle, Terrie is not heard from again and presumably joins the Kirkwall Circle, is made tranquil or is among the mages executed by Meredith.