Just guessing of course but possibly at Leath's School of Food and Wine in London. I know she's a fan of Motor Yacht Loon and follows their Youtuber chef @TheCrewChef (as do I). The Loon Yacht chef vlogged her experience at Leath's where she attended classes in order to complete her Ship's Cook Assessment. It's funny, when I was watching that vlog, I thought this is probably something Marie wants to do. .Anyone want to query where her cookery class is as it's probably best to locate herself not too far away from it. Will it be like the flower arranging class, really only an intro. Why not attend a cookery school in France and feed SJ's guests (guessing this is reason) with some French food with locally available produce. Will they expect her to follow recipes?
I checked Leath's course calendar and they have a course starting on Janurary 8, 2024 and the course sounds like it would fit what Marie might need. It's geared to people with some experience in cookery but who want to hone and "up their cooking game." It's called Chef's Skill Course and runs from Jan. 8 to Feb. 27 at about £5000 (https://leiths.com/course-calendar/?d=2024-01).
I guess we'll see because I'm sure Marie will be posting on her Insta in the future. Love a little detective work on a dreary, cold Sunday.