South Africa were thumped 51-33 in the second Test at Wembley Arena, after going down 49-38 in Bath on Sunday, with the host nation taking an unassailable 2-0 lead in the three-match series.
While the Proteas had a good start, holding their own for most of the first quarter, and put up a fight in the final 15 minutes, they were completely outplayed in the two periods on either side of halftime.
“I’m extremely disappointed, but congratulations to England who played extremely well,” Kotze said.
“We showed moments of brilliance, especially in the first quarter, but I think we became over-cautious and we lost some rhythm in the flow of our game.”
Kotze insisted her side could not continue to rely on major games as learning curves, and needed to close the gap on the top teams in the world.
South Africa, are ranked sixth, while England are third.