Vitani would require a mate with patience, understanding, and strength to match her own. A wimp or weaker character just won't do. xD
[quote="Kopa23"]The directors of TLK said that Nala's father was either Mufasa or Scar.[/quote]
This wouldn't make sense, though, because then Kiara would be mated with her uncle. And the creators changed Kovu's lineage while making the movie, from Scar's son to just being Scar's heir, to avoid the whole inbreeding issue.
And if we go by how real lions act, most animals avoid inbreeding when possible, and lions will kick males out of the pride to avoid inbreeding, as well. And male lions are usually kicked out around 3.5 years of age.
Personally, I think Nala's father was an unnamed lion who mated with Sarafina before being booted from the pride.