He never said she was cool, he was presenting what he remembered of her, which was a new thing for him. The long lost friend he just remembered, and she ended up being a BFF on Riku's level. It wasn't so much him saying how cool she was, as much as describing why he thought that.
One of the main issues why I prefer the SoNami relationship over SoKai - we know the basis for it. Sora told us how it started (from the group), how it developed (being BFFs with both him and Riku), and then the 'conclusion' (the promise he made her).
SoKai we get to see them drawing in the secret place... and that's it o_o
Not that I blame her that much, even Sora and Riku needed the FM+ to show flashbacks for them, and then Santa mentioned some stuff in KH2, but Kairi never got that :v bleh, SoKai </3
Due to length.
And I still can't believe I'm ranting to you about this.