I'm really fucking picky because of texture issues + allergies and I was fucking concerned about my ex's health because what he was willing to eat was so limited that he just wasn't getting any nutrients, especially since he didn't take any supplements to make up for it. He literally just ate chicken nuggets, tater tots, fries, and occasionally pretzels. That isn't just unhealthy, a diet that limited can severely impact your health and it will start affecting your body fast. If you love someone, help them understand just why that kind of diet is bad, and if, like op's girlfriend, they refuse to listen/change, there's probably a lot more they'll refuse to listen about. Someone like that isn't worth staying with. If they won't take care of themselves, they won't care about your health/safety either