We made one using two very wide straps, which were used to go under each of the hind legs. The ones we used were 6 inches wide and about 6 feet long. I believe they are sold at many Farm supply stores. They were each attached to the tractor bucket so that we could lift the cow. These were around the hind legs. A cow gets up with her hind legs first. In our case the injury was paralysis due to a difficult calving. When we raised the hind end, the cow was able to get up in the front on her own. A few days of helping her rise and stabilizing her with the tractor while she built up strength, was all she needed to recover. I understand your cows injury involves the front legs, so our sling would not have worked. Perhaps two wide straps that come from the shoulder and down around each leg and back to the shoulder. Attach all four ends of the straps together over her shoulder and then hook that to the bucket of a tractor or a strong rafter if she is where that is available. Start lifting slowly with the tractor bucket while someone stands behind and gives strong encouragement for her to get up in the back. If you can get her up, then leave her standing with the straps to catch her when she starts to go down.
Sometimes I think they just give up when they have difficulty rising. She may have the ability to stand now, but you need to show her it is possible. If she can stand with some help, she will likely improve with time. If she just hangs there in the straps and makes no effort to use her front legs, it is probably time to give up.
