How do I help???

[bgegmum]

So my friend was at a healthy weight last year. But she then lost her mum and had some other emotional issues and since then has went downhill. She always called herself fat but was far from it and claimed I was skinnier than her. I am overweight/obese although I don't look it I am and I hide it well.
She has just mentioned to me that people keep commenting on how skinny she's looking and if she's on drugs. She has recently realised how underweight she actually is and asked me to tell her the truth.
I haven't commented much on her weight unless she claimed she was fat. So I told her she had lost a lot of weight and I've been worried about it.
She's admitted she has a "problem" but she said she's getting better herself.
I asked straight out if she had an eating disorder. She said she didn't know all she knows is she has had a problem for a few years but this year the emotional stress has got on top of her. She is adamant she doesn't need my support (although i think she's trying to cover the fact she does) she said she doesn't like talking so won't even think about professional help.
My mum had an eating disorder when I was really young and I can remember screaming and crying begging her to eat. I was just a child so this is quite hard to see my friend going through the same thing and brings back a lot of heartache for me however I want to help her. I just don't know how.
Should I leave her to her own devices or try and guide her to professional help?
How do I know when she needs immediate medical intervention?
I'm seriously not sure how to handle this whole situation
I do apologise in advance for words like "fat" and "skinny" I know they're not ideal but this is the way my friend talks about weight