I hope that things will go well. I have a young adult daughter and the way in which I have been able to help her is by building a strong, kind and loving relationship and forgiving the terrible things that the ED sent our way when she was very ill. And reaching out when I can to help her in whatever ways she needs support.
Yes you have leverage now and you can model compassionate and caring behavior for her and the fact that families support each other through the difficult times. It probably was not easy for her to make that phone call and ask for help.
Since you don't know the status of her weight you don't know whether she is ok or not. She might be fine. And she might not be. But is seems that you will need to get your husband to come around to having her at home. You have the opportunity to heal the relationship and can stress that to him if you think that might help. You might want to wait until you see her and speak more about it but there are some things to consider:
You have already stated the ground rules about eating, taking meds and seeking treatment if she needs it, which are sensible. And you may want to encourage her to find work, or be in school, or volunteer for some causes she is interested in if she is well enough. And make sure that she is getting any medical care which might be needed.
We had very simple "contracts". More of a series of requests and agreements for example when she came home from treatment, and then when she went off to university. I did not ask her to sign anything since that could have given her the opportunity to say no. I did give her a written paper with our requests.The requests were things like: open communication, weight maintenance, full nourishment, allowing her team to communicate with us if necessary, staying in treatment as long as she needed to and listening to what her team recommended for her.
best wishes for your reunion with your daughter.