Sarah Lucas b1846 Westbury on Severn (General)
Perhaps this is your Sarah Lucas?
FreeBMD
Births Jun 1846 (>99%)
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Surname First Name(s) District Volume Page
Lucas Sarah Westbury 8 471
I can not see a baptism on this site for this Sarah.
The marriage certificate of Sarah to Francis Chapman should give her father's name and occupation, which will assist further research.