Momentum Proteas fast bowler Shabnim Ismail claimed four wickets to help dismiss the West Indies for a modest 174 to earn South Africa a comprehensive six-wicket victory in the fourth and final one-day international at the Wanderers in Johannesburg on Sunday.
The victory earned the home side a 2-1 series win following a washout in the first game, a tie and a Super Over victory for the tourists in the second game and a 96-run win for the SA Women in the third match on Thursday.
Laura Wolvaardt (23) and Tazmin Brits (20) gave the run chase a solid start but Steyn, whose classy 52 came from just 73 balls and contained four fours, seized control while Luus anchored the innings facing 80 balls and hitting three fours and a six.
Both were dismissed by veteran offspinner Anisa Mohammad shortly before the game was won, leaving Chloe Tryon to finish the job in style with four boundaries in a quick fire 20 not out from just 17 deliveries.
Ismail removed both openers after the West Indies had chosen to bat first with Rashada Williams (6) beaten for pace and bowled while the big-hitting Deandra Dottin was smartly caught at extra cover by captain Luus for 36 after a second-wicket stand of 65 with Kycia Knight.
Dottin finished the series with 235 runs at an average of 78.3, including a career best 150 not out in the first game.
Left-handed Knight top scored with 48 from 76 deliveries (6x4) before tamely slapping a short, wide delivery from seamer Tumi Sekhukhune to Ismail at point.
Hayley Matthews was dismissed by a stunning, one-handed catch at full stretch by Laura Wolvaardt at backward point off the bowling of left-arm spinner Tryon and the rest of the innings was a struggle for the tourists with the hosts maintaining a tight, single-saving field.
Despite dropping no less than five catches the Proteas nonetheless dried the runs up with spinners Luus (8-0-24-0 and Tryon (6-2-12-2) particularly effective.
Ismail returned at the end of the innings and collected another two wickets with her extra pace to finish with 4-44, the seventh four-wicket haul of her career.
Both teams head to New Zealand next week ahead of the World Cup which begins on 4 March.
SOUTH AFRICA: Tazmin Brits, Laura Wolvaardt, Andrie Steyn, Sune Luus (capt), Mignon du Preez, Chloe Tryon, Nadine de Klerk, Trisha Chetty (wk), Shabnim Ismail, Ayabonga Khaka, Tumi Sekhukhune
WEST INDIES: Aaliya Alleyne, Deandra Dottin, Rashada Williams, Kycia Knight, Hayley Matthews, Mandy Mangru, Shemaine Campbelle (wk), Cherry-Ann Fraser, Afy Fletcher, Shamilia Connell, Anisa Mohammad (capt)