let's talk about the fact that she has a yet unseen keyblade wielding style as is evidence in this photo. (No worries, it's not a spoiler since I'm not giving context)
Everyone shown is in their combat pose. Roxas, Xion and Sora all wield in a similar fashion and are posed as such. Also worth noting is that Roxas and Ventus are both shown, designating them as separate entities. But most important is that Kairi is in a pose completely unlike that of any wielder thus far. Nomura has shown in the past that
every damn thing in these games is worth analysis so her being in that pose can't just be overlooked. What's most interesting is that the pose it most resembles is the stance Sora takes when locking a keyhole.
This could either mean that Kairi is either taking a mosting non combative stance in KH3 or it could mean that she's going to be a WMD. Strange jump? Well there was one time that Sora used the locking light attack in combat:
The final finishing blow used to take down Xemnas is the light of the keyblade used to unlock or lock the keyholes of worlds.
Now, if this pose is showing that this is Kairi's standard method of attack, well then. Good fucking luck Xehanort.