I would like to thank you all so much for your thoughtful replies, this is the most supported and heard that I've felt in a really long time.
Regarding D's weight she had gone from 42nd percentile before AN to 56th percentile this last April in terms of BMI, but even though her weight has remained stable she's down to 51st percentile because she's 6 months older. I'm now back to trying to increase her weight. She was hugely resistant at first, but she has been accepting the larger snacks over the last few days. So that's certainly something to keep working on.
Regarding how difficult it is to get her to eat, this potential school is not really set up to treat eating disorders so they would just send her back home to me if she doesn't eat. She knows that she has to eat to be able to go so she has been eating her lunch under their supervision so far (trial days). But I have no doubt that they will call me at some point telling me that she's refusing to eat and I will have to pick her up. They seem to be ok with this arrangement though. Her previous school doesn't have the resources to monitor lunches, let alone call the parents of every kid who didn't finish their lunch. But this school is so small and teachers already have to sit with some of the children who have sensory issues anyway, so it's not a stretch for them to supervise D's lunch.
Foodsupport_AUS, thank you for highlighting that keeping D home is still treatment. I have been so busy trying to get her any professional help that I can find, but my H is right in that we're not sure that any of it has had an impact. While I agree with him, it feels like her anorexia is still so severe and mental health so poor that maybe she requires more than we can give her at home....but what? I haven't come across any professionals with a magic wand yet, and some of them do more harm than good. The dietician at D's last partial hospitalization program asked if we could skip morning snack because she kept forgetting to give it to her since she was busy at that time of the day. ?!?!?! Then when I replied in no uncertain terms that "no, we couldn't skip it", she still went around my back and just started giving it to D together with lunch, theorizing that the total calories were the same in the end. By the time I found out about it, D had become hugely resistant again to the psychology of morning snack. And this is supposed to be an eating disorder center. I complained to the person in charge about it, but they didn't seem overly concerned. sk8r31, you're right, thinking outside the box is key in these situations. I think that I'm coming to terms with the idea that a way forward doesn't have to be how I imagined it. I had always assumed that D would go back to her old life (school, friends, hobbies), but she has given up all of those and shows no sign of getting back into these things. We also can't seem to get to the bottom of it. But when we take her to the school parking lot, she just starts to hyperventilate and scream at the top of her lungs. So we can't even get her through the doors. She just says that she doesn't want people to see how she looks different, but keeps saying that there was no bullying of any kind or any other issue before. I did, however, find out that the other girls at her lunch table were encouraging each other to eat a "healthy" small amount at lunch (in their words). So I suspect that the eating disorder was somehow tied to feeling socially accepted by others, and now she feels like she wouldn't be if she goes back. We suspect that at this point she really wouldn't have the skills to navigate through those situations in a healthy manner anyway. We did consider homeschooling, but my husband is a cancer patient and I need to work in order to make sure that he has access to medical care when he needs it. In terms of interests, D has given up all hobbies (like playing the piano). We can't get to the bottom of that either. She can no longer articulate any desires for the future, which makes me so sad.
I have to admit that the more professionals we see, the more alone I feel. They're all first overly confident that they'll get D sorted out in no time, then they eventually realize what they're actually dealing with, at which point they pretty much find a way to say "We don't really know what to do but your daughter is too oppositional for us and we've never seen a case like hers, good luck with that. Good-bye." One psychiatrist in particular just lectured us last week for 2 hours on how my D has become so oppositional, that even if she wanted medication he wouldn't give it to her because there is no point in treating her until she's no longer oppositional. No suggestions, no brain-storming, no support from him, just criticism. Oh, and he told D that she should just listen to him because he's got a PhD...I couldn't believe it.
mjkz, thank you for making me feel like I'm not the only one with these issues related to oppositionality. She wasn't like this before AN, but it's a trait that she seems to have developed over the last few months. In fact, teachers use to describe her as a "rule follower". We have tried several "contracts", only to have D backtrack the very next day and not care one bit whether it was written down on paper or not. D also figured out that the inpatient clinic won't take her if her weight isn't low enough, because we did try to send her back to inpatient after she stopped eating for a day and they wouldn't take her. We did call a truancy officer to try and talk to her, but we found out that they also have no way of physically making someone go to school if they don't want to. People from the county came to talk to her to tell her that if she continues to refuse to go, she could even get sent to a truancy program or end up in foster care (they were trying to scare her a little I think). She still wouldn't go to school. So taking her to this other school does put a financial strain on us and it's certainly a stressor, but H feels that it beats having her sit at home doing absolutely nothing for days on end because that has been terrible for her self-esteem. I'm glad to hear that the oppositional behavior got better with time, it gives me hope.