I just hope beyond hope she hasn't got the same problem as our beautiful 16 month old Amber - a spinal abscess, which in our case, over only 3 to 4 days, became worse and worse (the paralysis) and eventually we were told we had to put her down as she wasn't responding to antibiotics. I got a post mortem done which is how I know for sure it was a spinal abscess, on the area above her back legs 3 vertebrae from the end, and they also said they was some signs of bone decay suggesting the problem might have started weeks earlier. What we will never know is how on earth the abscess started - we check all our pigs daily and cannot recall any wounds, bites, scratches or injection sites on her that could have become infected. However, don't despair, your pig may not have anything so drastic. Also, on the same day the vet attended our Amber, she had been to see another pig with exactly the same problem, and that particular one responded to the antibiotics and has pulled through, so back leg paralysis/spinal abscesses are not always fatal.
The really important thing, especially if the leg dragging and/or paralysis gets any worse, is to make sure she gets adequate water to drink, as she wont be able to get to it herself, and food if she will take it - and also make sure if and when you call the vet that they give her an antibiotic suitable for the possibility of a spinal abscess. Just for info - Amber never had a temperature, or rashes/blotches, or sneezing or discharges, and the only thing we can recall before she started dragging her back legs was what appeared to be a mildly sprained foot, but no wounds of any kind, then an occasional slight wobble as she walked around, all within 3 days of the paralysis starting. She was however off her food, but only after the leg dragging started, not while she was slightly lame. Also normal weeing and pooing until that point. The very best of luck, and I really hope your pig gets better quickly, but I thought I should warn you just in case it is the worst - Tamsaddle