'The death certificate also says Sarah is the widow of Edward Llewellen.'

This may be one to consider:-

IGI Individual Record FamilySearch™ International Genealogical Index v5.0
British Isles
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EDWARD LEWILLEN Pedigree
Male Family

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Event(s):
Birth:
Christening:
Death:
Burial:

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Marriages:
Spouse: SARAH COBLEY Family
Marriage: 19 OCT 1794 St Thomas' Church, Bristol, Gloucester, England

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Messages:
Extracted marriage record for locality listed in the record. The source records are usually arranged chronologically by the marriage date.

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Source Information:
Batch No.: Dates: Source Call No.: Type: Printout Call No.: Type:

M018256