How do you think Simba would react if Nala was ambushed by Zira's pride instead of him? What would he do if he saw Nala walking injured from the "fight" (like Kiara saw him in SP)?

Simba would send his army of pridelanders to whoop Zira's pride's ass and Simba would tore her to shreds for good!
When it comes to just Zira vs Nala? Nala would easily kick her ass for being the larger female that eats right and weighs more. Zira is nothing but skin and bones like Scar.

I think Simba would be super extremely pissed at them, and probably at Kovu too, and I think he would be worried and call for help immediately (like Kiara did for him in SP) and try to help her meanwhile.

I think Zira would probably take more enjoyment in attacking Simba. But if she did attack Nala. Kovu and Simba's pride would be mad. Kovu and Kiara would have tried to help her. But it would have been possible for Kovu to also be blamed by Simba. Not so much as By Nala or Kiara.

I think Simba would firstly sent Zazu for help, he would be with her some time, and then he would his pride and him, with no injuries and extremly pissed, fight Zira's pride and then Zira would pray to die!