The letter referred to above (from George's son to John's daughter, obviously following a request for information) is as follows:
"...
My Grandfather (I am the fourth son of George Craven of Birkenhead formerly of Wakefield, your father’s brother) had
Charlotte, died two months ago
Fanny died in Jamaica, left no family
Bessy died at Wakefield, leaving four children all married with children
John (your father)
Mary, died young single
George at Birkenhead, 5 sons and 2 daughters living
Nancy, dead 15 years since, leaving 10 children all married all [with] children but two
Hannah Mirfin (a widow) at Oulton has six children, five married with children
Susanna Wormald at Flanshaw, nr Wakefield has four children, one married.
…"
Thus we know that Fanny/Frances is part of this family. From this information, and from details I had already found, is where I got the dobs, etc. The others given in ColC's post are cousins. I have tried looking for emigration to no avail; if she was already married, it would be impossible unless I knew her married name. There does not seem to be a plethora of information on BMDs in Jamaica!
Frances had written to one of her aunts to find out such information about her family and to tell them of the death of her father some 6 years earlier. John, her father, has a long story and a very varied and courageous history, but suffice to say it's too involved to go into here. However, he left Wakefield sometime around 1795-1804 (when he married and lived in Alnwick). Obviously, he had more or less lost touch with his family. I think Frances was about to emigrate to Australia and needed for whatever personal reasons to get information and thus wrote the letter of enquiry.
Don't worry too much about this one, Chatters! It was just another fishing expedition in case someone could stumble over something that I can't (I can't afford to subscribe to all the genealogical sites!). Thank you all for your efforts anyway; as always, you all go the extra mile.