Elizabeth Pierce is generally listed as b c1829, Llanidan or Newborough
The 1841 census entry for Thomas Roberts, smith, in Newborough also has this household at the same address
Margaret Jones - 40
Mary Roberts - 15
Elizabeth Roberts - 13
John Roberts - 10
Elin Roberts - 6
There's a nonconfirmist record, certifying that Elizabeth Thomas, daughter of Thomas Roberts and Margaret Jones his wife, who was daughter of Richard Jones, was born in the place commonly known as [not easy to read, but could b Yr Efail - the Forge] in the parish of Llanidan in the parish of Anglesey on 25 March 1829
Potentially some patronymic naming here - which could explain his mother being a Jones. Potentially Catherine Pierce is thomas' granddaughter