People in recovery from an eating disorder need the kind of help most people would need when healing from a chronic, severe illness. Family members and friends can offer love and care while showing expressing their concern with time and attention. Most loved ones wouldn't interfere with the medical and clinical plan other than to be sure that care is adequate and proficient.
However, it is hard for families and friends to resist meddling in treatment for eating disorders. In general people have very strong personal opinions and feelings about food and weight. Despite every intention of following clinical care, loved ones have ideas about what recovery ought to look like.
More often than not, those opinions come from a place of love. Adding seemingly useful advice to a treatment plan can seem helpful and constructive.
However, the person with the eating disorder almost universally experiences the guidance as intrusive and judgmental. The advice comes across as harshly critical and detrimental and is counterproductive in ways that won't make much sense to the family member or friend.
Clinical guidelines and meal plans come from an objective caregiver with experience and knowledge about how to approach eating disorder recovery in a caring but non-judgmental way. There is no way for a loved person in the patient's life to express opinions about food that are purely supportive.
The easiest way to explain this paradox is that for a person with an eating disorder, discussing food and meals is the most personal, exposing and potentially shameful thing to open up to others. Nothing else compares. For people without eating disorders, food is largely impersonal, but people with eating disorders would discuss anything else first. So offering love and support can help the loved one use her own strength for recovery. Objective opinions about food only leads to a feeling of exposure and shame which only strengthens the eating disorder.
The basic premise is that support for someone in recovery needs to involve love and care. Advice, like with any other illness, belongs to the clinical treatment team, not with loved ones.