Please could you give other useful info from the marriage certificate. Ages of bride and groom and their addresses. Names of the witnesses. No reason to think that the mother would be a witness, more likely a sibling.
Possible for Mary Jane from 1901
26 Church St, Penydarren RG13/5030 folio 84 pg 21
William H Griffiths head mar 37 coal miner hewer
Elizabeth wife 34
Wyndham son 7
Mary J dau 5
Annie dau 3
all born Merthyr Tydfil, all speak both Welsh & English.
Same family in 1911
https://www.familysearch.org/ark:/61903/1:1:XWXW-LRMso the C Griffiths could be older sister Ceridwen
1901 she was helpfully with her grandparents
1901 10 Plantation St RG13/5030 folio 141 pg 7
Thomas Davies head mar 57 coal miner b. Pembroke, S?
Mary wife 57 b. Glam, Morristown
Sarah dau 19 dressmaker b. Penydarren
Ceridwen Griffiths grand daughter 9 b. Penydarren
In other years, place of birth for Thomas shows as Blackmoor Hill or Narberth.
Likely birth reg for Mary Jane Griffiths sep qtr 1895 Merthyr Tydfil vol 11a pg 719 mother's maiden name Davies
marriage reg William Henry Griffiths march qtr 1890 Merthyr Tydfil vol 11a pg 708 with Elizabeth Davies on the same page
William Henry's family in 1871
77 Church St RG10/5400 folio 75 pg 21
Wyndham Griffiths head mar 39 ironstone miner b. Glam, Aberavon
Ann wife 33 b. Carms, Llandovery
Mary A dau 12
William H son 7
James son 3
Edmund son 1
children all born Merthyr Tydfil
birth reg William Henry Griffiths june qtr 1863 Merthyr Tydfil vol 11a pg 380 mmn Dawkins