Her mother's birth year is estimated. Geni.com says "1317" but Genealogics says her mother's father died "Abt 1253", so we show a compromise until more evidence arises. A discussion has been started on Geni.
http://thepeerage.com/p11345.htm#i113446 - citing (1) Jirí Louda and Michael MacLagan, Lines of Succession: Heraldry of the Royal Families of Europe (2) Source: The Complete Peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, Extant, Extinct or Dormant, by G.E. Cokayne; with Vicary Gibbs, H.A. Doubleday, Geoffrey H. White, Duncan Warrand and Lord Howard de Walden, editors