Mom will only eat restaurant food. What can I do?

My 85 year-old mother has been not eating and drinking much for almost a year now. Most days now, she only eats one tiny meal and about 12 to 24 oz. of beverages. She will ONLY drink soda (that's not the problem, though). I've been doing ANYTHING for this woman to keep her strength up and I've been buying her whatever she asks for, which is usually takeout. She will NOT eat home cooked meals. She will throw it in the trash. I am a good cook, so it's not that (lol). She'll have nothing to do with supplements and all of that. Dr. told me to give her anything she wants to eat at this point, just to get calories. She's not in the "danger zone" yet -- she still has to lose another 30 - 40 pounds before she gets underweight, but here's the thing: She's always asking for takeout food that is only sold in large portions, and usually they're costly. She will only eat things like pizza from her favorite local eatery (they don't sell by the slice), or bbq ribs, rotisserie chicken, Chinese, fried seafood, etc. It's getting so that she either thinks she wants them and won't eat them at all, or she'll eat just a tiny portion and the rest will entirely go to waste -- so I end up eating all the leftovers and I'm gaining a ton! Not even food I like! I tallied it up for last month, and she ordered $189 worth of takeout food. I'm gaining all the weight that she's losing. Now I KNOW that I'm completely going CRAZY. No one in their right mind orders that much takeout in a month. But that's what I've been doing, so she'll eat SOMETHING! I've been told that this is common end-of-life behavior to have no hunger or thirst. Please be kind and don't make fun of me or insult me.