While there are numerous legends surrounding her, how she came to train Hadral, and what happened to her after she and her son were separated, none of these are planned to be addressed directly in the Fatebound series. These can be developed and added below.
Muriel is the name most commonly used to describe the mother of Hadral. She is mentioned in the prologue of the Epic of Hadral, but all other references to her are commonly considered to exist outside of canon. This, of course, depends on who one asks - various branches of Ristarianism and Neophaelism hold some set of these stories as canon, or at least as much canon as anything else.