From Shotgun Shuffling
What exactly Dheu is hasn't been fully explained, and may not be. Rusche simply stated Google "dheu meaning". Doing so puts the Wikipedia page for Death, which contains a blurb stating dheu is etymological great-grandparent of the term "death" and it means "Process, act, condition of dying".
Dheu was the first character to appear on the D52 linked off the cast page. Rusche states here that Dheu is one of only two characters on the D52 that is summonable. The second character is speculated to be Kimberly whom Pumpkin tried to summon as her [attack in the cosplay battle, though since Kimberly arrived deceased, this may or may not be the second summonable character.
Rumor - Commenter TheLastOutlaw replied to Rusche here referencing Dheu as the father of Ashliii, which would explain her last name but raise other questions. This author comment would also jive with Dheu being Ashliii's father.