There are a lot of comments recommending euthanasia, and I probably agree with them. As much as the OP wants to save the chicken it may not be possible or kind to do so, given her catastrophic injury.
OP, think about what sort of life a one legged chicken would have and how much extra care and attention it would need every day. If she survives, can you devote that much time to her on a daily basis, for perhaps 5 or 6 years? She will be disabled, picked on by other chickens, and stressed because of that. You may have to make her a little wheely contraption, and how will she bend down to peck food and drink? She won't havr any balance, and she will never be able to scratch around again with just one leg. Imagine all the poop cleaning of a wheely sling, and the dirty sore butt she will get with risk of flystrike. You may have to isolate her, so have you got the space for that? Lone chickens don't do well because they need company. All sorts of things to think of, if you can make her well again.
I'm so sorry for her and for you. Its a horrible situation to be in. One I was in myself recently with a poorly chick. I know how hard it is struggling with that big decision.
Have you at least given her some baby aspirin yet? That is important to reduce her suffering.
And she will try and act normally because she is a prey animal. They hide weakness in order to protect themselves. Don't take her appearing OK as evidence that she feels fine and not in awful agony. She will likely be harbouring an infection in that wound and will need antibiotics quickly or face a slow painful death from sepsis. If you treat her rather than euthanize, then get AB for her.