Matilda's face contorts in the way it has almost every time she's been forced to make a decision on her own over the past entire hellish day. And the Wizard is asking her this. Hesitantly, as if afraid for the judgment she might receive, she responds.

"Just plain. I don't really care for sweet things."

She then pushes up her pajama sleeve and pinches her arm. She had to be polite and respond, even if it's just a dream. But maybe this will wake her up.