We had a raccoon hit our coop last weekend and had two chickens, about the same age as yours, get big open wounds. One had her back torn open and her leg "depantsed". The other had a gash ripped open in her side. I thought they were going to die or have to be put down. It was very gruesome. I took them to our local emergency vet and they stitched them up really well. We've been giving them topical and oral anitbiotics and anti-inflamatories. In addition, we've been keeping them inside and restricting their movement somewhat.
Neither are out of the woods totally yet but they have improved quite a bit and are trending in the right direction. If you can manage it, I would try to get the wounds closed up because of the risks of infection and maggots and because they heal so much faster if they are closed up. I understand if you can't though because so far this raccoon attack has cost us about $2,300 in vet bills for the two birds.
I hope your hen pulls through!