I don't know if you live in a country setting, but if so, maybe check for snake bite or possibly some sort of poisonious spider bite? Dunno, I would think a snake bite would be noticible, but I am not familiar with types of snake bites or spider. But when you mentioned swelling that came to mind.
If you live in the city I guess you can rule this out, but just wanted to mention incase she wasn't checked out. My dog suddenly lost use of her back legs and was in sudden pain and it was "Addisonian Crisis." Please talk to your doctor about that disease to see if they checked her for it. I hope all works out. I know how awful this is when going through this.
MO
Wow, I guess you can't leave web addresses...Let's see if this will work: Petfinders (then a dot) then com. ;)
Here's what you need to do while you wait on someone's advice: Contact Breed Specific (Greyhound) Rescues. Ask them these questions...One way to locate some: ****.*** On their opening page, there is a tab that says shelters. Click on that tab. It is done by state...Find every Greyhound Rescue that you can and post these questions. There will be contact numbers (Either phone or email) listed with each Rescue or Shelter's Name. This will be a place to start...Hope this might help.....Good luck........I'm praying for you both......... Karla
P.S. Has he been checked for Lymes Disease? Some of this does fit.......