The Proteas comfortably beat India by 115 runs in Leicester on Saturday to keep their semi-final hopes alive in the tournament.
South Africa suffered a 68-run loss against England on Wednesday after the hosts put on a record total 373/5 and Van Niekerk says her team was hurting on after that big defeat.
The Proteas' bowlers certainly put in a better effort against India on Saturday, dismissing the Asian side for just 158 chasing a target of 274 with Van Niekerk leading the way with figures of 4/22.
"I'm incredibly proud of the team, that's the response that any captain wants to see after a loss like that," Van Niekerk said after the game.
"It's a very tough tournament, it's hard on the body and it's a long tournament as well. We're not used to playing tournaments this long so I'm glad they took that time.
"I'm glad that they hurt (after the England match), because today they came back firing."
South Africa's next game in the tournament is on Wednesday against Sri Lanka at Taunton.