My friend went through this with her daughter. Her daughter is fine now, 20 and in college, studying to be a nurse. She's doing great. I have another friend whose daughter wasn't eating, not due to anorexia, but due to Celiac and a food motility problem that had her feeling really ill all the time. She's also doing well. Therapy was key, and I also worked with her to teach her to prepare gluten-free foods she liked so she could take control of her own eating. That's stopped the fighting between mom and daughter. She was 15, turning 16, when I worked with her. So your daughter might not be quite as adept in the kitchen yet, but perhaps you can consider a version of this, helping her to prepare basic foods (or having some neutral person do it) with no expectation that she must eat.
The psychological part was the big hurdle. So hearing that you have a great team is wonderful. Do work on the therapy more than you worry about the calories. I know that's impossible in many ways, but I think it may be the way you have to focus.
You can also sneak a lot of nutrition into foods. I work a lot with protein-rich, nutrient-balanced powder which can be put into yogurt, smoothies, milk, water, and even sprinkled on a lettuce leaf or a quarter of a turkey sandwich - whatever the kid will eat. Rapid absorption at the cellular level helps people get the most from the nutrition, even in small amounts. So you could try something that is highly absorbable but not thick. I'd stay away from things like Boost and Ensure - those are chock full of emulsifiers which makes them hard to digest. They fill the person up too, which makes them less willing to try other foods because they just don't have room or they feel kind of nauseated. I've gone to a lot of nutritional and food science trainings, and there are a lot of people with anorexia/bulimia success stories. So there is hope!
My advice, based on the experiences of friends as well as the lectures I've attended, is to stay focused on the long term and not today's calorie intake. Therapy can help your daughter figure out how she can have more control in her life without restricting food (if that's the issue) or redefining her body image (if that's the issue). Also work with the therapist yourself. She won't just one day start eating again. It will be gradual. You will have some successful days, and some setbacks. As hard as it is for you to back off, you really have to. But this is all new to you and you will see that a good therapy program will work with the family and not just the child. Don't be afraid to ask for help, and don't feel that this is up to you to solve.