You are most certainly not being unreasonable, stress is one of the worst things for your health and capacity to heal and she is causing you a lot of stress and unhappiness. I totally agree that you need to focus on getting calories in whatever way you can and to all the food police out there I would like to share that my daughter was a fitness fanatic that exercised everyday, ate only organic, home cooked, low fat food, drank only water, herbal tea and matcha, didn't smoke or drink alcohol and is riddled with multiple health conditions including the worst grade of endometriosis as well as osteoporosis (exacerbated, if not directly caused by over exercise, being underweight and excluding dairy and most meat for nearly two decades).
Of my two best friends, one is a hugely overweight, ex-smoker, recovering alcoholic who was diagnosed with cancer 16 years ago, told by the first three doctors she saw (I was with her each time) that there was nothing that could be done but to make her comfortable. After her op she was told that she was too ill for chemo, it would kill her and then whilst on chemo she developed multiple pulmonary embolisms that nearly killed her and incidentally, she too was told to eat whatever she wanted - advice which she thoroughly took to heart. My other best friend, like my daughter, was a fitness obsessed, vegetarian, who collapsed up a mountain whilst walking with family and was diagnosed with terminal cancer.
She survived a little over a year and her and her husband were so bitter about the "unfairness" of healthy people who had "done nothing wrong" succumbing to cancer whilst "unhealthy, irresponsible people" got to live - literally their words. It was very difficult not to completely lose it with them but I understood they were overcome with fear and grief, but to hear this kind of judgement and bitterness over and over was literally like listening to a religious fanatic who had lost their faith because they had thought that their piety would exempt them from all the ills of the world and it repelled me that they were implicitly saying it should be my other friend dying and not them.
Is it sensible to try to eat healthy and get some exercise? Of course. Is it healthy to be an orthorexic food puritan that is indoctrinated by health guidance and internet nutritionist gurus? Most certainly not.
My aforementioned best friend is still beautiful, imperfect, joyous and going strong (touch wood) and long may she remain so. My daughter has given up her puritan ways and has a devoted, loving relationship with Willie's chocolate and Lindt caramel bars. Unfortunately she's just as unhealthy but she enjoys life more.
I wish you a full recovery and a long future filled with happiness and Green and Black's chocolate. Be positive and refuse to give up, that's what will get you through more than anything.