Watching my mom harm herself and not being able to stop it

My mom is anorexic. Her anorexia had begun decades ago, long before me or my sibling (we’re both adults now) had even known the term “anorexia”. It also became progressively worse over the years. When I was a kid, she stopped eating meat and some vegetables with relatively high caloric value, now she refuses to eat parts of berries she perceives as “too filling”. I don’t know how much she weighs, my dad tells it’s slightly less than 50kg, but I don’t believe it. I have seen her during our video chats. I doubt she weighs even 40kg.

While me and my sibling were growing up, we were berated for “overeating” and becoming fat. It had only occurred to us that this dynamic is deeply unhealthy when we both became working adults. We also suspect she has undiagnosed depression, which doesn’t help things.

Over the years, any attempts to point out that she should eat more (admittedly, pretty clumsy, since we kids and other adults knew nothing about mental health) were never met kindly. If somebody tries to talk her into eating a bit more, or expresses worry about her health (she is extremely thin), she closes up and rejects/ignores anything being said. While me and my sibling are being open about our mental health struggles and being honest about therapy, psychiatric care and medications we need, the idea of meeting a mental health professional is being rejected by her aggressively.

I know what I am going to say next shows that I am kinda shitty person, but it is what it is. I thought I had made my peace with her condition years ago, because she refuses not even help, but the idea she may need help. It is not in my power to make her want to get help, and as somebody who suffers from mental health issues, it is my belief that you can not be fixed if you don’t want to be fixed. So I chose being able to have relationship with her instead of trying to pressure her into getting help.

However, recently we were made aware of a very acute health issue she had, which almost became life-threatening. It is not related DIRECTLY to her anorexia, but it was made worse by severe lack of nutrients she subjects herself to. The issue was exacerbated by her refusal to drink for several days. What infuriated me most is that she received lots of infusions due to dehydration and started complaining that she feels better and tries to drink… but her body feels heavy and she dislikes it.

I feel like piece of shit for not being there for her and not knowing how to be there for her. I feel terribly for not doing something, anything to make her wake up and stop torturing herself. At the same time, I feel furious, because she actively refuses any help, she objects to being treated (for any health-related issues), she rejects any attempts to talk. I feel bitter. I feel helpless, powerless, like I can only watch how she withers and disappears. I don’t know what to do or what even to say. I feel guilty. And I don’t think anything is going to change.