[TW: eating disorder]
First, I would not recommend bringing “other ways of losing weight” into the discussion at all. What your friend needs is support in who she is right now and always - she needs to own her body and herself. She needs help.
But she also needs to want to help herself. You can’t make that decision for her.
It is hard to watch someone you care for head toward a path of destruction. I know the feeling very, very well. After dealing with it in many ways and many different situations, I’ve determined there is absolutely nothing to do except show support, explain your thoughts, express your feelings, and urge that they seek help.
I am obviously not a professional but if she is starving herself to lose weight and denying care for medical conditions, that tells me she may have a mental illness. If she has an eating disorder or is mentally unstable, she is ill, and needs treatment.
Passing judgement on her for making unhealthy habits (not to imply that you are, but you might be, I don’t know) is not what she needs. She needs to know that she’s a good person - she is worthy of love, health, and happiness, and she deserves to be good to herself. And she can do that by getting help, because she doesn’t deserve to take it all on herself.
If she doesn’t respond well to the conversation and refuses help, you have to let her make her own decisions. Be there for her as much as you can, but not at the expense of your own mental health and well being.
It is hard. I wish I had a better answer.