I always assumed that Vitani is the daughter of Zira and a rogue lion.

I take more in theory Scar and Nala are the parents of Vitani, but gave the puppy to Scar Zira, or any other lioness mother Vitani may be, he just gave Vitani to Zira. But since it's up to decide a fan, thanks for the help

As Brown Wolf said, it is up to fans to decide. You have plenty of articles exploring all these options. Since movie does not really tell clearly, so it can be interpreted in many ways.

Also I believe more in number 3, since I believe Kovu and Vitani have same father.

It's questions like these that have no right or wrong answers. Many theorists go at it this way:

1. Vitani is the daughter of Scar and Zira, which is something I can go along with because I like it.

2. Vitani is the daughter of Scar and maybe a pridal lioness through force - 'cause let's face it, Scar was mad - and was raised by Zira perhaps because the mother died in childbirth or something like that.

3. Vitani is the daughter of Zira and a rogue lion.

Also, it is possible that Nala is Vitani's mother, by Scar, despite their makeup differences. Hello! Scar is an Outlander, so Vitani, - if Nala is her mother - could have gotten her Outlander looks from him.

Either way, any one of these theories could be correct, but officially, we will never know because Simba's Pride is a failure as a sequel, among other things. So, no one is right and no one is wrong. It is what it is and there is no right or wrong answer.

Yes, they hate each other. But maybe Zira made ​​Vitani hate Nala?

If i know one thing, Nala isn't vitanis mother, because in the 2nd movie, they hate each other. Plus Nala was a pride lander and vitani a Outlander.