Why don't you believe (or not want to believe) that Xion's has her own keyblade? Are you adverse to it for some reason?
1) It's not just any random Keyblade out there. It's not like while sora has the KK that Riku has the WtD and Mickey has the IKK - that while is similar, is still different. It's the KK - something that seems to be Sora/Roxas dependent. Xion just popping one of her own out of nowhere seems unlikely to me, and is more than enough basis in and of itself for one to assume more than just a passing relation between "Xion's" KK and Roxas's KK.
2) Throw in the fact that thus far we've never seen them both wielding their KKs at the same time and you'll see why I'd sooner relate Xion wielding the KK to what happened between Riku and Sora in KH1's HB where Riku
took the Keyblade from Sora, leaving Sora with none.
3) Then we have Roxas asking if Xion can use the Keyblade too - as opposed to her
having one of her own.
It's "you can use it", not "you have one", showing that it's likely the same Keyblade, and up until then he went by the notion that like Leon in KH1, the Keyblade would run away screaming from most people back to its original owner. Xion managing to hold onto it would no doubt be a surprise.
I mean, in 'Another Report', Nomura said that there isn't one particular Keyblade for a particular realm, and there are "just as many [Keyblades] as there are qualified hearts" (pages 28 & 29, question VI).
Who are we to say (or know for that matter) that Xion's somebody (whoever that may be) didn't have a 'qualified heart' ,and they don't just have the same connection that Sora and Roxas had that was also explained in 'Another Report' (pages 28 & 29, question VII)?
And yet neither Aqua nor even Kairi (her being able to wield or not aside) - have had the
Kingdom Key. Roxas has the Kingdom Key because he's Sora's Nobody, and Sora is the one that the Kingdom Key chose. The only possibile way for me to accept Xion has her own KK is if she was created along with Roxas and Naminé, but seeing how Naminé doesn't have the Keyblade, I doubt Xion would've gotten it had she been born then. And then you once again come down to the conclusion that if Xion is
Kairi's Nobody, she wouldn't have gotten the
Kingdom Key, for she wasn't created from the
Heart chosen by it.
Just a question; no disrespect intended or attempted.
None taken, it's a legit query.