According to Medlands the children of Ralph de Mortimer and Gwladys Ddu were:
Roger, Peter, John, Joan, and Hugh.
No mention of Maud
Do any of the managers or Curator Erin Spiceland have any sources to support her holding this position in the tree?
Terry, I don't know. Ralph de Mortimer sounds familiar, but Gwladys Ddu does not. I don't recognize that name from my work in this tree. Perhaps her father was another Ralph de Mortimer? I cannot find the name of William's wife on FMG at all. His entry is here: http://fmg.ac/Projects/MedLands/ENGLISHNOBILITYMEDIEVAL3T-Z.htm#_To... (2d). I have just corrected his mother, as FMG says he is Roger's son by an unknown mistress.
Erin Spiceland, Gwladys Ddu is not a problem she is in Medlands as daughter of Llewellyn ap Iowerth and an unknown mistress and widow of Reginald de Braouse. The problem is Maud. She does not seem to be a daugther of Gwladys and Ralph de Mortimer nor wife of William de la Zouche. Do you agree?