Actually, SA, I think I have some more support for you.
In the released trailers including the one on the front page of this site, there is footage of Roxas fighting alongside, most likely, Xion in Beast's castle. But in the trailer, not only does Xion (presumably) only fight using magic, but she's not wielding the KK either. But, the scene that comes afterward (and seems to come next in terms of continuity) Xion is fighting Riku on the bridge with KK.
Of course, this trailer is old and Xion still has her hood up, meaning that at the time of this trailer Nomura and co. were probably still trying to keep her under wraps. But then, why have the scene w/ Riku anyway showing the KK? That's more support. There's also the possibilty that Xion was hiding her KK usage from Roxas, but there seems to be no reason for that at all.
Also, Riku calls the KK 'fake', meaning that, if it was stolen, then he was calling Roxas' keyblade fake, which we know it isn't. But Riku may have just been in denial about another person wielding KK while Sora was asleep.
Honestly, I think that ultimately Xion has (or rather I feel that she should have) her own Keyblade if for no other reason than the series, imho, needs a female keyblade wielder in the current timeline especially since Aqua's recently showcased awesomeness is practically choking me with excitement. But, I will conceed that all press releases up until now support your conclusion that the KK she uses in stolen.
In the released trailers including the one on the front page of this site, there is footage of Roxas fighting alongside, most likely, Xion in Beast's castle. But in the trailer, not only does Xion (presumably) only fight using magic, but she's not wielding the KK either. But, the scene that comes afterward (and seems to come next in terms of continuity) Xion is fighting Riku on the bridge with KK.
Of course, this trailer is old and Xion still has her hood up, meaning that at the time of this trailer Nomura and co. were probably still trying to keep her under wraps. But then, why have the scene w/ Riku anyway showing the KK? That's more support. There's also the possibilty that Xion was hiding her KK usage from Roxas, but there seems to be no reason for that at all.
Also, Riku calls the KK 'fake', meaning that, if it was stolen, then he was calling Roxas' keyblade fake, which we know it isn't. But Riku may have just been in denial about another person wielding KK while Sora was asleep.
Honestly, I think that ultimately Xion has (or rather I feel that she should have) her own Keyblade if for no other reason than the series, imho, needs a female keyblade wielder in the current timeline especially since Aqua's recently showcased awesomeness is practically choking me with excitement. But, I will conceed that all press releases up until now support your conclusion that the KK she uses in stolen.