My daughter is three and over the course of her life she has had perhaps 5 happy meals. One every six months on average. She's not obese, a little underweight

My daughter is three and over the course of her life she has had perhaps 5 happy meals. One every six months on average. She's not obese, a little underweight for her height in fact. I use it as a reward. It's a experience for her, the drive thru, eating with me, playing with the toy. The best thing about it is it's affordable and she will actually eat the food. Why is this a bad thing that needs to be regulated away?