Theoretically a cleric. Theoretically.
Trissa is (or was?) a cleric of a goddess of Joy, or so we were led to believe. She joined the party when summoned by Earl Dregard. However, she departed it when her lightning tattoo trapped her in a mysterious elven prison. Unlike the rest of us, who leave the prison, she has not.
She and Cassiel did not get along well, and Cassiel was consistently suspicious of her behavior. Triss sold a Pickled Punk to an underworld dealer and encouraged the drug trade in Whitehorn.