I think it's time girl's night became a potluck. Everyone brings their favorite dish, and worries about their own dietary restrictions.
I agree. A year and a half is a long time for you to bear all the burden of feeding everyone.
You can still have fun making food, etc., but you need to open it up if only so that you can say to her, in private:
"You need to bring something you can eat. I'm not anymore going to cater to you with the menu for girl's night.
"And you need to develop your own willpower, and stop yourself from eating carbs that are bad for you."
And then when she has a panic attack over the truffles, get annoyed. Treat her like the drama queen she is being. Be the teensiest bit scornful: "You know you have diabetes--nobody made you eat that. Enough already."
If she keeps going, get her coat, "Well, since you're not feeling well, I think we should send you home."
And I think you can say to her, in private: "your constant conversation about your dietary restrictions, and your panic attacks over the carbs you eat, are ruining the vibe of girl's night. Specifically, they're stressed me out. Please stop."
I do like the "I'm worried about your health in terms of your anxiety" approach.
But otherwise, here's a very simple tactic that fits with my "Don't talk about your boundaries; live them" philosophy.
Tell everyone that you want them to bring a dish--it's too much for you to provide all the food every time. They need to bring something.
Then make whatever the heck you want. Fish with walnuts and onions, is my vote. And fresh veggies.
And then EVERY time she makes the tiniest comment about food, especially negative, but maybe even neutral, or has a panic attack or anything at all, look at her as though she has two heads.
And say NOTHING.
Don't even beandip. Say nothing.
Don't know how to do that look? Find a teenager and ask them to teach you.
And never, ever discuss a menu in advance with her again.
It's basic behavior modification