One of my best friends is starting to develop severe anorexia. What should I do ?

talk to an adult

in person

Tell her mom

Or yours

Or your teacher if he/she is nice

get her help, go on websites to help her recover, tell an adult

Unless your friend's parents are really negligent, they will have noticed. Teachers will have noticed, too. I know it's probably hard to hear, but there isn't much you can do for your friend. People with eating disorders are extremely resistant to treatment, and will lie or isolate themselves from concerned family and friends. Just be present and patient. Don't talk about anyone's body, body image, or food. (Almost everything you might say could fuel the disorder, no matter how pure your intentions.) You can't give your friend the professional help they need, but you can love and support them.

Tell someone about it.

@Lucy 👏👏👏 beautiful

help

@Lucy Well said. Just reiterating: tell, tell, tell. Parents, counselors, teachers... keep telling until they help your friend.