Contact her family or someone with more authority to push her into doing something. If you have urgent concerns about her health, you can call emergency services and explain all you have here. The plus side to the extent of her condition is it’d be reaaaaally hard for her to “lie her way out of it”. They do physical exams. They’d see the damage in her throat and esophagus, check her weight and fat percentage, and if necessary they’d also check her vitamin and adrenal levels. If she’s been fainting then she likely has adrenal fatigue, which means that her adrenals can crash and she could die. Thankfully, its not exactly like having a heart attack, usually. People die a bit on the slow side from eating disorders, meaning she’s going to get really bad and get herself hospitalized at some point, which in turn means it’d be hard for her to deny that anything is wrong with her.
Eating disorders like this bring a lot of blatant physical effects. Greying of the skin, yellowing or glazed over eyes, brittle and yellowing nails, an odor that can become pungent, dry hair and hair loss, fainting, bone loss, muscle weakness, spasms and severe cramping, loss of her period, decreased lung function, heart irregularities, structural damage to the throat and esophagus, seizures, numbness and tingling, memory loss and dementia like states.
The list goes on and on. My point is, it’s not something you can simply just hide from medical professionals. Tell people close to her about what’s happening, tell her what you said here and reiterate that you need her to be healthy, because simply surviving isn’t sufficient. She deserves health, and she deserves to feel okay, and those are very real possibilities for her with the right help. And, again, contact emergency services if you feel like she’s going to faint/has fainted or do any further harm to herself.