Rolling pin, wooden spoon, silicon spatula, measuring spoons. Maybe a loaf or shaped tin, or tin for muffins or little tart shapes. Good knife, whisk, set of cups (measuring), apron, (maybe chef;s hat to match?), oven gloves,
What about cake tin liners - either for loaf or round tins? Lakeland certainly do those. And I agree about fancy cupcake/muffin cases, and different sprinkles etc. If she is happy to make her own icing, perhaps some good colourings (2-3 different colours), or maybe some nice flavourings (like real vanillla extract, orange water, rosewater, decent mint etc.) or good cocoa and chocolate drops.
Icing bag and nozzles?
I am just thinking of things I use a lot, and things that DD likes to have of her own (she's 6 but makes cookies and a chocolate cake by herself now (well, I still have to help measure, and I do the oven) and has quite a few of her own tools).
And it could all go into a large airtight box/fancy tin to hold the goodies, or a large mixing bowl, as the "basket" of a hamper...