All I can think of offhand is that you might find her birth if you know which church to write to.
With her father's name, you might find a listing of the plantation name in the yearly Directories of British Guiana (available at some libraries worldwide). The name of the plantation could possibly lead you to land/tax records located at London's Public Record Office.
Other than that, the Colindale Library in London has a pretty good run of Guyana newspapers from that time. That's a real needle in the haystack search, though fascinating!
And there are a few books (with some names) about Guyana history, which you might also locate at a large library.
Guyana is very difficult, as so much has been lost and there is little local interest in genealogy today. I don't really know what is to be found there except for the vital records starting in the 1880s. We need a fact-finding mission (not to mention money for preservation)!
Sorry I'm no expert, but hope this helps!