I’m trying to recover an illustrated children’s book from before 2005 or so. It was hardback, with a green cover, I believe. The illustration style was quite unique and lovely, almost Celtic? Lots of green. The main crux of the book was an alchemist/witch and her apprentice who she sends into the woods to gather needed ingredients for a potion or spell. It took place primarily in the forest, and one of the ingredients I remember was a specific type of mushroom. Other tasks involved something in a marsh/swamp, and maybe something about flying creatures? But what I remember most was the alchemist/witch. She had long dark hair.