I'm trying to identify a book I read in the mid-2000's in English, which I'm fairly sure was the first in a trilogy. I remember very little of the overall story-arc, but a few scenes stand out:
- The main character was a young girl who somehow ended up in a world that wasn't her own
- When she first came to this new world she was in a massive room that at one point had enormous aquariums for walls, filled with colourful fish
- In this world you could create matter somehow, or reshape things, and she was told if she was hungry to visualise food and it would appear - she visualised a chocolate sandwich, and while it looked perfect, it tasted like nothing because she hadn't thought of the taste when she called it into being
- There's a witch in the story, who has spiders in/around her mouth? And at one point the girl is terrified she's turning into the witch (her teeth are falling out and she's finding spiders in her mouth), but ultimately she realises it was her fear of turning into the witch that was causing this, as she was unconsciously transforming herself due to her fear, which only exacerbated the issue.
I've done a bunch of key-word searches in google but am finding it very difficult to track down.