Yup. At this point, his daughter is her own worst enemy. She cannot be trusted to take care of herself. She is lying to herself by telling herself she's still fat and that the anorexia is okay. Anorexia is illogical. Bony skeleton women are not particularly attractive (especially once you add in health complications from the eating disorder). Unfortunately, this means that you can't reason with her, just as she can't reason with herself. You definitely cannot trust her with her own health; that much is obvious.
Another thing you might consider (although it will be difficult with her college so far away) is her friends. Are they contributing to her anorexia? Or could they help her to keep it under control (after all, they'll be around her a lot). If her friends are encouraging her to be anorexic, she needs to stop seeing them. If they are a problem, you should not let her return to school right away.
Our situation, thank God, is not extreme yet. In fact, we have caught this rather early, it turns out. Treatment and monitoring are underway. She is eating. No tricks. Eating! She attends a Catholic university. There is much help for this sort of thing...and there is, comparatively, not that much of this sort of thing there. Thanks.