There is every chance she could live through this. Chickens are amazingly resilient. When you say you can see into her neck and chest, how literal are you being? Can you actually see organ tissue hanging out? I am a person that thinks if you can actually see organs in the open, then that is a catastrophic injury that there is little chance of coping with. If organs are visible then culling is probably the best option for all involved. The chances of infection settling in, the length of convalescence, the pain and suffering, the isolation of a flock animal... better to cull than to put everyone through this.
If you really want to save her then I can offer some advice on wound healing. First, she needs to come inside out of the cold. Hay is not going to cut it when you have a bird as wounded as this. Bring her inside and clean the wound with either peroxide or betadine tea (one part betadine to 10 parts water). Really clean it well. I like to use a turkey baster to really get into the wound. Next cover it in some sort of wound dressing. Any one of the following will work- Neosporin, Bag Balm, Blukote. Then settle in for a long convalescence. The wound will need to be cleaned with weak salt water and dressed each day and as needed. Don't even bother trying to cover the wound- bandages will not stay and will likely be picked at by her. Watch for signs of infection- angry redness, sudden increase in oozing, hot heat radiating from the wound, nasty odor. Feed her lots of protein rich foods to help aid in healing. Once she starts healing maybe bring in a friend from her flock to keep her company. Flock animals heal faster when they have a friend close by. Keep her isolated until she is nearly healed. And then begin re-introduction(s).
I hope she's OK. Good luck.
