At 1000 cals daily intake whe's probably sabotaging her metabolism but she's probably not putting herself in physical danger.
It's not really your place to butt into her dietary decisions. I know that sounds harsh, and I know you only have her best interests at heart, but it's her life, her body, and her diet and she doesn't appear to be doing anything dangerous, at least not that I can see based on your original post.
"A mistake is not failure but feedback. -Rod Gilbert"