Anorexic friend?

My friend has lost a lot of weight since middle school, we're sophomores in high school. She seems to be obsessed with dieting and exercising. She's doing 300 squats a day and doesn't eat anything but salads and fruit. She doesn't even eat gum bc of calories. Shes probably around 120 lbs and has an app to track her health. I'm becoming worried for her, what do I do?