i’m surprised at sam’s answer, and think you’d need to ask a shaila before telling her mother even.
It’s not always a good idea to tell her to eat, and there’s that risk of her getting upset with you over it. Encourage her to tell her parents and/or doctor. If she’s nervous to, show her the benefits, alleviate her fears if you can. She likely won’t be able to stick to a diet with a therapist and nutritionist’s help