The result means that the South Africans - who suffered a rash of injuries leaving them with only nine fit players on the final day of the tournament - remained winless at BC Place and finished in 12th place at the tournament.
The first half was a ding-dong affair with both teams guilty of handling errors and it was no surprise that the scorers were not bothered at halftime.
Great Britain started best in the second half, scoring two tries for a 12-0 lead, but as in all other games, Nadine Roos was not going to be denied.
Roos, who scored in all four of their earlier matches at the tournament, did so in the final match as well, but it came too late to change the result.
Scorers:
South Africa 5 (0) - Try: Nadine Roos.
Great Britain 12 (0) - Tries: Kayleigh Powell, Jasmine Joyce. Conversion: Emma Uren.
