I'm sure Nala isn't Vitani's mother.
And bytheway, Vitani has more like a purple nose, right?

And Nala's nose is more like..pink/red , dark pink? xD
And IF she would have gotten Vitani with Scar then Vitani must be older, right? Well ofcourse I don't know how old Simba and Nala were when Kiara was born but... xD They look some older though, so..
And in the beginning from the movie she's still a cub like Kiara.
Sorry if someone said this already. ^^''
I think it's easy to explain it's obvius Nala isn't Vitani's mother.
Vitani have looks from Zira also in my opinion. I don't see any of Nala to be fair.