This article is about Willa's mother. You may be looking for the episode called "Celeste".

Celeste was Willa Frost's mother, Arthur’s Daughter and the wife of Isaac Frost. She went into a coma while giving birth to Willa. Isaac was desperate to save her and sent her into the Realm in an effort to bring her back, which ultimately killed her. Isaac wouldn’t accept that she was gone, and built the Hollow Sky organization on the belief that if he could get into the Realm, he would find her there.