Anyone who's never been exposed to an ana-chan of this magnitude is going to find it highly frustrating as well as horrifying. Her commitment to remaining ill is rivaled only by the most stubborn of level 5 hoarders. She's nothing but her illness at this point, and that's all she'll ever be for the rest of her days.
She's not going to be institutionalized against her will, but even if she were, what then? You can't let her leave, she'll just return to the way she was. So she's stuck in basically a nursing home and being force fed until her body eventually gives up on her. Frankly, that's not much better than starving at Disney World. If she were an animal, she'd be euthanized, but she clearly wants to keep existing in this state, so there's no real option but to allow her to live the remainder of her life the way she chooses. Some people don't want anyone's help, and forcing them to accept it just delays the inevitable.
And yes, she's not in her right mind, but we don't even know if there is such a thing for Eugenia. She's never been well, even when she seemed to be improving. Her brain has been consistently starved throughout its critical development period from adolescence to age 25. She's quite literally brain damaged at this point and I don't think she's able to get better. Any hypothetical time period where an intervention might have worked is long past.