2 week old puppy has very swollen back legs, which appeared to be blister like, and just today the huge blisters ruptured oozing out very dark blood like pus? What could this be? I drained all liquid out and cleand thouroughly with peroxide. Can someone help??

The puppy needs to go to a vet. Sooner rather than later, or you will come home to a dead pup.

Yes, I will be taking her to the vet, but that would be on Monday as all businesses are closed here in mexico do too a religious holiday. I´m just curious and worried, what can she possibly have? Is it some kind of genetic disorder or some kind of infection? Your help is greatly appreciated, thank you

By chance could she have been burned? Could be an insect bite, an infection, anything! Since she is not able to go to a vet soon, keep it clean, keep her hydrated, keep her comfortable. Is there other puppies? If so I would separate them in case it is contagious.