From FreeBMD:

Births Dec 1877 (>99%)
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BLEWETT Fanny Eliza Westbury S. 6a 253

Births Mar 1880 (>99%)
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Blewett Fred Westbury S. 6a 263

Births Sep 1882 (>99%)
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Blewett Frank Westbury S. 6a 237

Marriages Mar 1874 (>99%)
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Blewitt William Westbury S. 6a 393
Harris Charles James Westbury S. 6a 393
Probert Eliza Westbury S. 6a 393
Sparrow Fanny Westbury S. 6a 393

Don't tell me - more non conformists?!
There are 4 pages of Blewetts (various spellings)on the Gloucestershire Archives Genealogical Database www.gloucestershire.gov.uk/archives - 40k
Some from Cinderford/East Dean locality but not the names you want! Probably not transcribed yet.
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This could be Fanny in the 1901 Census:

Results in the 1901 Census for - Fanny Blewett
Fanny 1878 Glostershire Cinderford Croydon C B Croydon Cook Domestic

...and maybe this one for 1891:

Results in the 1891 census for - Fanny Blewett
Blewett Fanny 15 Lambeth 24, Kennington Second