My 17yo dd struggles with eating, it wasn't full blown anorexia but nearly so, back when she was 12/13/14. It was very scary, she was self harming in other ways too. I took the approach of being very, very calm about it, and focused on what she could manage rather than what she couldn't. She could still drink, so to keep her hydrated and her stomach full, I bought her a variety of teas, soft drinks, cordials, coconut water, etc, and some new cups, water bottles, etc. She also learned some self care activities that helped her learn the importance of looking after herself- at the time she could only manage to wash her face and clean her teeth every day, she was very, very low.
During lockdown she started experimenting with baking, so she would try new recipes a lot (not necessarily eating the cakes, but sometimes).
I made the choice to refuse to battle her over eating, and told her as long as she was staying hydrated I didn't have a problem- the human body can survive a long time on little food, but not water. So it wasn't an emergency as far as I was concerned. (Of course I was constantly worried, I just stayed calm with her)
I did my best to keep lines of communication open, and she would tell me when she was eating less or self harming more, and we would discuss what we could do to help her feel better or what her triggers might have been. School was a huge trigger for her, and I ended up home educating her for a year and a half, including lockdown time.
She's much much healthier now. She's got a job, she's in college, and her eating habits are better. She still can't eat if she's anxious about something, but sometimes a glass of water is all it takes to get her back on track. When GCSEs were on the horizon, we talked about how she would spot the signs of slipping back into old habits and how we could help if she did, but she managed really well in the end.
There were times I felt like I was taking a huge gamble with this approach, and I felt scared a lot. But I forced myself to trust her and she told me more and more what she was going through, as well as therapy. That calm trust built up between us and she found a way through it.
This is so hard op. Don't beat yourself up. Hold your dd close and tell her through your words and actions that you are on her side every time.