According to Keats-Rohan, in Domesday Descendants, Vol 2, Bertha was the daughter of Richard FitzPons (or Filii Ponii), Lord of Clifford, Herfordshire, and sister of Walter de Clifford. That's where the name Clifford comes from, FitzRichard is obviously from her father..
She married Elias or Helias II Giffard, and had two sons; Helias III, and Walter.