[The Australian Panther]

It seems that at this point, the intention was just to put Zola and Twilight together on one side purely to create romantic tension. The way Zola is portrayed here is cringeworthy, definitely not politically correct by today's standards.
From a narrative point of view I would guess they enjoyed writing Twilight, since they have continually highlighted her hijinks. She has more dramatic possibilities because of her background, so it makes sense that she would come to have a more dominant role to play than Zola. Pity. Nice girls finish last?

Link to the book: Buck Ryan 67 - The Case of The Nervous Hero