Elisabeth, I am late here but I wanted to offer commiserations -- and some words of hope.
First, on the diagnosis...my cousin is celiac but it was not diagnosed until she was a young adult (after years of ongoing health issues and also anxiety). Of course she was scared and disappointed when she learned what was going on -- but what a difference it has made in her life. It has been wonderful to see how much stronger and healthier she is now.
On the cooking...it will definitely be a learning curve for you and the entire family, but it's not too bad once you get used to it. My DD was gluten free for a while (for other reasons) and so the whole family got used to eating this way. I bought a rice cooker (brilliant appliance if you are going GF) and I got onto Gluten Free Girl: https://glutenfreegirl.com (fun backstory...you must read it when you get time!) and got a few decent GF cookbooks, and pretty soon we were doing just fine.
There used to be a fabulous GF bakery down on Cornwall...Oh -- found it: https://www.pannerizo.com
It's not cheap but it is delicious stuff, and if you take her there a few times and bring home a few treats, she will probably be able to handle the whole idea a bit better.
I used to see a lot of older people in there when I'd go, looking shell-shocked but also elated. I struck up a conversation with one of the older ladies once. She told me she had just come from her doctor's where she got the diagnosis, but her doctor told her to go to Panne Rizo immediately on leaving the office. It was the doctor's way of saying, "You will not have to give up the lovely treats you enjoy."