I have confronted her several times and encourage her to eat more to put some meat on her bones. She gets pretty upset with me and promises to work on it, but I haven't seen any progress in the last six weeks. She's reluctant to see a therapist or a doctor. The fact that she gets upset when you express obvious interest in her health status is not a good sign. Such defensiveness was a common finding in athletes I've worked with, who later turned out to have rather severe eating disorders.
Threats only make the situation worse.
Since it may not even be the problem here, your problem is twice as hard. You don't know whether there's something else going on, with fear as a factor in her trying to ignore it. Be there, and really work on having her visit her doctor. And be sure the doc knows what you've observed. All rights reserved.