Firstly, being there for her is the main thing and it seems that you are so ❤. I am so sorry that you and her are going through this.
One thing I have found is that some people (who are normally brilliant around MH issues), seem to think that because eating is an essential behaviour we are choosing to partake in these behaviours because they cannot visualise why one would deliberately not eat (or choose to spend all of our lives ruminating over food or choose to deliberately eat the lowest calorie option even if it isn’t liked). Just like people with depression can’t choose their maladaptive depressive thoughts, people with ED can’t choose how to eat (either via restriction or bingeing). When she isn’t eating or she spends time before or after a meal (maybe adding calories), that isn’t her wanting to do that.
Even my very understanding and tolerant wife has lost the plot in the supermarket while I look up the calories. It’s taken tears in the aisles from both of us to show her that I don’t have control over that behaviour. (I’m not saying you will do this- but she may encounter it elsewhere).
Having taught young people with ED, I know there is hope and recovery is possible. You both can get through this together. You’ve come so far already. If you say something that isn’t right (which happens), then it’s a learning curve for both of you (like with anything in life) and you move on. I hope I haven’t spoken out of line. Thinking of you both ❤