cornsnake, it's all very well being happy with her at any weight but she wants to be fatter. Do you not want her fatter? There are men who would want her fatter. I don't know if you are just trying to sound virtuous for loving her at any size but really the point of being Feeder and Feedee is you both want it. If you are just going along with her desires JUST to please her then it's not mutual.
Yes obviously it's bad for her health to get that fat but she is weighing up her desire to get fatter with her health concerns. You really don't seem to excited by the idea of her getting fatter and only concerned with her happiness and her health.
Some people here might think that entirely right that your only concern is for her needs and desires and not your own but in a relationship she would be wanting someone who actually desires her to get fatter.
It's gotta be a two way mutual thing. Clearly the balance is difficult if she's the one getting fatter and you're the one running around for her but the desire for her to get fatter has got to be something you both share.
So in conclusion I actually think it's right for her to get fat but not for you. You might need to consider separating so that she can spend her life with someone who shares her desire.