Hi Terry
I wouldn't be concerned about the Fanny and Frances - I have so many family members baptised with a shortened form of their name (probably by the father

) and called by the full name and of course the reverse. FreeBDM is virtually complete for the approx time of her birth and there are no other possibilities that I can find. You could search the full registers for perhaps 2 years around your date - but I doubt your will find another person - however, you probably need to do this to ensure for yourself that the 1880 lass is yours. If you know the 19th July is correct, then purchasing the certificate will confirm whether or not this is the date. I don't see alot of other options, if you currently have no idea of the parent names.
I have a number of misleading facts on some Australian relatives - a gravestone in Victoria states born 1832 - the parish record in Scotland says 1830 (perhaps a deliberate lie to the Australian wife - she was significantly younger

)
Dawlish is very close to where the family I found were living in 1881, so that fits reasonably well. Was there some reason you thought the family came from Somerset rather than Devon, because all the place names seem to fit Devon - My UK geography is not the best.
Did Edith come to NZ by herself? or with other family members - this would help to determine if we found the right family. Alternatively, We could check 1901 to see if she is missing from the family I found in 1881.
The registration district of St Thomas makes no mention of Dawlish, but it was replaced by Exeter. Kenton is part of this District.
http://www.fhsc.org.uk/genuki/reg/districts/st%20thomas.htmlI shall check 1891 - perhaps the family moved to Dawlish.
Trish