...my god, you really don't get it, do you?
Xion said that she was receiving something from Roxas, to the point it was filling her up. That was the point of the analogy with the water, a bucket filled to the brims it was already spilling. Either Roxas was filled up with Sora and he was spilling over to Xion, or Xion herself was "full" now - the process of her being changed by the Memories and thus her getting powers or what not - probably the Keyblade - was nearing completion.
She then asked Roxas what she appeared like to him - when still with her hood on. One might conclude then that she changed - and Roxas was the one that changed her, by her Memories.
I know your English is bad and all, but this is ridiculous.