She may have broken something in her spine and the nerve signal isn't able to get to her legs. It's imperative that you get your dog to a vet TODAY. The longer you wait, the less likely she'll ever have the use of her legs.
A dog who can't feel its legs or feet stands to get very ill. They get cuts in the numb parts of their bodies that get infected. It's not a pretty death.
Please don't wait any longer and find a vet. Nobody on the internet can give your dog the treatment she needs. When injuries are this serious (and hers is) you've got to go for the hands-on professional approach.
That is definitely something you'd need to consult a Vet about. Just because you felt no broken bones does not mean that there aren't any. Sleeping under a dumpster? That doesn't appear to be a safe place for a dog to be sleeping none the less. I'm sorry this may come off extremely rude, but if you don't have the money to care for an animal, perhaps you should not own one. Like I said, the dog needs to see a Vet.