I want to find the family tree of (the surname) Hefer. Am looking for
a woman called Anna Louisa Hefer (nee) originally from Johannesburg in
South Afica and a member of the Dutch Reformed Church

To assist a researcher, you should add more details. Approximate time
frame of Anna Louise? Was she from the 1700's, 1800's, 1900's? Where
did she move to after South Africa? , etc.

 A quick search at Ancestry.com shows 812 hits for HEFER surname, and 
6 hits for Anna Hefer.

 A search at genealogy.com shows about 150 first names for the surname
HEFER, with ANNA having 3 hits (1 in International & Passenger records
& 2 in US census)

 Both of these are subscription sites, so you'll have to subscribe to
actually view the info.