Could Nala be Vitani's real mother?
As we know lionesses become sexually active at age 3. Perhaps Scar had at Nala before, Vitani being the result, but after finding out Zira's son Kovu wasn't his own he tried to seduce Nala and, since he had already had a cub from her, though it would be reasonable to make her his queen. Nala however refused and ran away. Since Vitani was of Scar's blood Zira accepted her without question.
Lionesses become receptive when current cubs die, grow up and leave, or when they are seperated. She would've been in heat again by the time she met Simba which is why while Simba was trying to be friendly Nala was acting rather flurtatious. It also explains that look (and lick) she gave him during CYFTLT. Simba and Nala mated in the forest and Nala was probably planning to stay there (which is why she was asking Timon and Pumbaa about his whereabouts. Also in a deleted scene Nala was going to stay with him.) there him until Rafiki informed her he went back and of course she goes as well.
During the hyena/lioness fight Zira couldn't risk her cubs getting injured/killed, if Scar should win the fight against Simba so she and Nuka took Vitani and Kovu away from the fire and the battle. Word got out Simba had won and Zira as well as the other outlanders had nothing else to believe except Simba had killed Scar. As for Nala, by the time the war was over her daughter was already gone, which explains her bitterness towards Zira when the first meet in SP.
It's actually not an outrageous idea.
Nala could give Vitani her pink nose, light coloration, eye color, eye shape, rounded cheeks.
Scar could give Vitani her nose shape, dark eyeshades, earstripes, smile, sharp teeth, long maw, anatomy, extended claws, paw color, and freckles.

[img]http://www.mylionking.com/resources/site_images/lk_screengrab_624.jpg[img]

Of course there are other possibilities.
ZiraXTojo=Vitani
SimbaXZira=Vitani
ect.