Thanda, nobody, least of all Zille, is defending Apartheid. Like Nazism it is indefensible and cannot on any moral basis be defended, and amongst Whites  Zille was foremost and courageous in condemning it, long before it became fashionable with the virtue signaling crowd. 
Many Blacks on the other hand have climbed on the Zille bashing wagon, not because of her silly tweet, but precisely because and only because she is a White person in a prominent position.  Now that's racist, Thanda.