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I would have this evaluated by an ER vet tonight. The fact that it's cold worries me. If the blood supply has been compromised, then it can start to decompose and become septic very quickly.
I would want to put her on IV fluids to help encourage circulation and do physical therapy on the leg through the night. If the blood flow returns, then great. If it continues to be a dead leg, then you need to consider amputation before it gets infected.
I hope this helps, let me know if you have any other questions.