A horse that's a 3 really isn't that far gone that you need to take extraordinary measures to get them back.
The first thing would be to set her up by herself to protect both her and horses already on the property from anything she might be harboring. She needs to see them but not have contact with them. Moving is stressful so don't add to it by introducing herd dynamics. Grass hay is the only thing you should start her on. Know what a flake weighs. Give her a flake, she cleans it up, give her another in 2 hours. Keep feeding her 2-3# of hay at short intervals. Adding a dose dose of a probiotic the first week will help her utilize what you are feeding by repopulating the bacteria in her gut. Give her a few days than combine meals, say 5# hay at one feeding 4 times a day. You want to know how much she is eating (as opposed to just offering her freechoice where it's impossible to know) so you can adjust her caloric intake. Start her concentrates. Deworm her after a week. From there, what you do and add to her diet is going to depend upon how she responds. Adding oils, alfalfa ect might be unnecessary.