I looked up ARFID and it sounds like just being picky.

I was a picky eater when I was a kid, I would generally only eat plain hamburgers, French fries, cheese or pepperoni pizza, fried chicken or macaroni and cheese

The only condiments I would eat were ketchup or ranch. I wouldn’t eat anything with sauce. I wouldn’t eat vegetables, etc.

That being said I grew up and got over it. You didn’t fuck up by taking her to a farmer’s market, your girlfriend fucked up by never growing up and learning to eat real food like an adult.

You fucked up because you have enabled her like her parents did, by allowing her to eat like a child and normalizing her dislike of food. I wish my parents would have been better about forcing me to eat more things when I was young because even though I will eat many more foods and I am not afraid to try new things, I still have bad eating habits many years later.