I think it just happened, like they didn't had any intentions on battle each other before hand but winded up fighting each other দ্বারা running into each other on the battlefield. If they did have intentions on fighting each other Nala would of been in the movie আরো and talked about Vitani with আরো negativity.
Nah honestly everyone was in the heat of the moment and Nala was probably fired up with zeal ready for battle. BUT! On the other hand Vitani maybe have tried to instigate a fight with Nala that's why she made the মতামত she did আপনি know "how's your pretty daughter Nala?" But that's a different theory. :D