I think my friend is anorexic?

One of my best friends has recently lost a dramatic amount of weight and you can really see it in her body and her face looks sunken. She is 15 and repeatedly refuses chocolates and high calorie snacks- and skips out on meals. She told me her parents are aware of it and take her to the doctor to check her weight however she seems to believe everyone is exaggerating the situation. Her parents give her £5 for school dinner money and i always see her ask people for change for the note (perhaps to pretend to her parents that she bought something). We went to a curry restaurant the other week and she didn't eat a single thing. i have became genuinely scared for her health. It is now noticeably visible that she is severely underweight and i was wondering if there was anything i could do about it considering i am her best friend. thanks.