Eloise Stemhower is a minor character in Trollhunters.
She was born in 1894, but then was replaced by a Changeling. She is still alive and a baby. She resided in the Darklands' Nursery for almost 122 years since her birth. Her status is currently alive because NotEnrique and Chompsky saved all the babies from the Darklands.
She makes a more prominent role in The Book of Ga-Huel, where Jim receives dreams and memories of him encountering a seemingly random baby familiar while he was finding Enrique in the nursery. When he finally remembers that Eloise was a Changeling Familiar in the Darklands, he realizes in the process that his new school librarian, Ellie Stemhower, is a Changeling Polymorph.