[TigerClaws]

She acted in the film. Dancing substitute used for full body shots.

So what?

Stunt doubles are used all the time in action flicks.

[hecht]

Stunt doubles are frequently used and are credited.
This case is another Millie Vanillie

[FrdmLvr]

Natalie Wood’s singing was even dubbed-over in West Side Story.

[truthguy]

She acted in the film. Dancing substitute used for full body shots.
So what?
Stunt doubles are used all the time in action flicks.

Ordinarily you would be right and I'd agree with you, BUT in this case the promoters of the film made a VERY BIG DEAL about Portman doing the vast majority of the dancing. I have a friend who is a trained dancer with many years of experience and she said at the time that there was NO WAY Portman could have learned to dance like this in the time allowed (if ever). So maybe those who produced the film lied and Portman went along.