Hello

I just thought that perhaps Mary had moved with her parents to Aberdare, and then met Thomas. I think that is more likely than a Llanboidy girl meeting a Llandybie boy in Carmarthenshire, but I may be wrong.
There is one example of such a Griffiths family moving from Llanboidy/Llanglydwen to Aberdare, who appear on the 1851 census.
Mill Street, Aberdare
James Griffiths Head age 42 born Llanfrynach, Pembrokeshire Hooper
Anna Griffiths Wife age 44 born Llanboidy, Carmarthenshire
David Griffiths Son age 22 born Llanboidy, Carmarthenshire Miner
William Griffiths Son age 14 born Llanglydwen, Carmarthenshire Miner
Mary Griffiths Dau age 9 born Llanglydwen, Carmarthenshire
Phebe Griffiths Dau age 7 born Llanglydwen, Carmarthenshire
Daniel Griffiths Son age 3 born Aberdare, Glamorgan
John Griffiths Lodger age 22 born Llanglydwen, Carmarthenshire Miner
William Morgan Lodger age 25 born Llanfrynach, Pembrokeshire Miner
Benjamin James Lodger age 27 born Llanfrynach, Pembrokeshire Carpenter
HO107 Piece 2460 Folio 449 Page 31
I knew that Thomas was a miner from the 1861 census

Best Regards
Morgan