Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern for your dog but I have to admit that I'd be a little worried, too, if she were either my patient of my own personal dog.
Swelling of this degree isn't commonly seen after a "simple" injury unless the leg is broken. If that were the case, then I'd expect her to be quite painful and I wouldn't have expected the swelling to reduce in size.
The fact that she now has a nose bleed makes me think that there may be something going on with her platelets such that she's not clotting properly. The swelling in her back leg could have been hemorrhage secondary to trauma; the reduction in the size could reflect resorption by her body if there's no additional trauma.
Decreased platelet production (aka Thrombocytopenia) can be seen with tick disease or autoimmune diseases or cancer or rodenticide poisoning and can be quite serious as you might expect.
I would dearly love to be able to provide over the counter treatment options for you but unfortunately, in a situation like this, she would be best served if you could have her seen by a vet as quickly as possible. I realize that my answer may not be what you want to hear but I would be doing a disservice to both you and your dog if I were less than truthful and honest in my response to you. I hope you understand. I also hope that this is helpful and that your dog is going to be ok. Deb