Save a dog

Saturday we went to rescue a dog I saw a few days ago with a cyst, big as a football, hanging under her stomach.
I contacted a rescue center and they came in the morning to pick the dog up.
We found a man that knows abot the dog, but she didn't show up.
We left him a rope and he promised to call when she was caught.He called yesterday morning. He couldn't catch her since she was biting wildely.
I hope the rescue center has an idea how we can proceed and rescue this dog.