Wolvaardt struck a brisk 67 off just 37 deliveries as the Proteas Women got to a total of 136-8 in a match reduced to 18 overs due to persistent rain before the start.
Annerie Dercksen contributed 26 in the middle-order but Proteas will be disappointed that many more batters got valuable time in the middle ahead of the global tournament.
Kapp then showed her class to defend the target, with figures of 4-24 as Irish were bowled out for just 120 in in 17.4 overs.
Tumi Sekhukhune took two wickets while left-arm spinner Nonkululeko Mlaba also struck twice in the wickets column as the Proyeas Women head into the World Cup wih some momentum.
The Proteas have another warm-up clash against New Zealand in Loughborough on Tuesday before starting their T20 World Cup campaign against Australia in Manchester on 13 June.
The Proteas Women will travel to Bulawayo in September for a historic first-ever T20 International series against Zimbabwe Women, with the neighbouring nations set to contest five matches at Queens Sports Club.
Proteas Women's captain Laura Wolvaardt has advanced to third place in the latest T20I batting world rankings following a brilliant home series against India.
The Proteas Women signed off their ICC Women's T20 World Cup preparations in emphatic fashion, sealing a 4-1 series victory over India with a composed 23-run win in the final match at Willowmoore Park in Benoni on Freedom Day.
The Proteas women fell 14 runs short despite a spirited chase against India in the fourth T20I at Wanderers Stadium on Saturday, though they continue to lead the five-match series 3-1.
