How can I help my [anorexic] sister?

My sister is 19 and has suffered from eating disorders for all of high school. She eats very little and throws it up. Last year, she hit a low and one of her ribs broke easily. It became clear then that she was anorexic.

When she got pregnant last year, she ate regularly for her child. Now that he's born and she isn't breastfeeding, she hasn't been eating as much. At 19 years old and 5'4", she wears a size zero (in America).

Yesterday, I asked if she was taking care of herself. She said no, and I told her she looks thinner. She then tells me, "that salad I ate today is the only food I've had in 3 days." She told me about the pants that she bought after having her son, and showed me how loose they are now. When she bent down to pick her son up, I could see her spine through the top of her shirt.

I'm really worried about her. How can I help my sister? Please. I need responses. I don't want to lose her completely. I don't know how to help her. I rarely see her because of her work schedule, so it's difficult to find the right time to talk to her. Do I sit down and have a talk with her (and support her)? Do I encourage her to see a professional? (She has postpartum depression and brought it up yesterday.) We've never been close so we aren't on "personal" terms. I'm surprised she even said what she did.
Please help me help her. Please, before it kills her.
How can I help my [anorexic] sister?
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