The raw translation is complete, which means I now have a decent overview of the recipes in the notebook. There are a total of 121 unique recipes. They fall roughly into these categories: Beverages, Cakes and Torte, Candy, Cookies, Donuts and Pastries, Jams/Jellies/Preserves, Mousses/Parfaits/Ice Cream, Pancakes, Puddings, and a Miscellaneous category. I updated the recipe page with the full list.
It looks like my great-aunt might have been working in the castle’s kitchen long enough to master pastries and move on to learning other skills. Included in the notebook are recipes for preserves, pickles, wine, and pickled herring. There’s even one for making beer out of rock sugar. I think I should try tackling that one soon, since you have to let it stand for a couple of weeks before you can drink it. I can hardly wait for berry season though. I love making jam.
I also have another clue. The inside cover of the notebook has an inscription:

Inscription on inside cover: Recipes for Frieda Möller, Wulfshagen 29.4.23, Friedel Möller, Gadendorf.
Wulfshagen and Gadendorf are in the same part of Germany as the village where Aunt Frieda and my grandfather grew up. Clearly, narrowing down the location is going to take a lot more research. Both covers also contain dates—April 29, 1923 on the inside front cover and 1922 on the inside back cover. That means she would have been in her late teens when she worked there. If she was preparing jams and pickles she must have work through at least one summer, as well. Perhaps she started as a pastry cook in 1922 and worked her way up to canning and preserves by the summer of 1923?