I guess it depends on why Kara is a glutton. Personally, I can think of three reasons: First, that more processed foods are more like the flavors of Krypton foods. In that case, I think Kara could come to a consensus on Lena's diet easily. Or, Kara needs a lot of energy, so she always turned to more caloric foods, which would soon be a challenge to any human diet. Or, Kara has a super sensitive taste buds. This would keep her away from more bitter or acidic flavors, which would also be easy to reach a consensus. Overall, I think she would support Lena in the best possible way for her to stay within her desired weight in a healthy way.
I always considered Kara's eating habits to be a caloric intake issue, but the taste buds thing is a totally interesting take. In which case the idea of her experimenting with making her own nutrition bars/snacks is especially sweet. Like... sure she wants Lena to feel healthy, but if she's going hard core into it then Kara is going to be right there with her making sure the experience at least has a pleasant taste.
