Okay, a few thoughts... first of all, is she getting enough vitamin C (it's vitamin C that pigs are unable to manufacture.) Like humans, guinea pigs do not make their own vitamin C. It needs to come from dietary sources. Without vitamin C, pigs can develop scurvy, which can cause a variety of symptoms, including paralysis/mobility issues. If she is not eating pellets (which are fortified with vitamin C) and she is not eating enough veggies that are high in vitamin C, she may be deficient and have developed scurvy. I would begin supplementing her vitamin C, both through diet rich in vitamin C and through supplementation. Pet stores do sell drops that can be added to water and can also be given directly to ill pigs via syringe. One of mine is actually on vitamin C now as a dietary supplement, as she is recovering from a respiratory infection. You would have to look at the dosing instructions, but the droplet she is on allows you to add to water OR to give 50 mg daily in a syringe, which is what we have been giving her.
Secondly, any change of injury to her back or legs? Any falls? Any exercise wheels (these are bad for the back, guinea pigs are not that flexible.) Any injuries of the back legs? Really, this is something that requires a vet assessment. Just like any other animal, pigs can injure tendons, break bones, etc. This will need to be assessed by someone who knows what to look for. She is potentially in pain, which should be treated for the sake of being humane to the animal. I know that if you're a minor, you're at the mercy of your parents... I'm a parent too and get how unexpected vet bills can take a bite out of the budget unexpectedly. But really, if you take on a pet you owe them proper care, including veterinary care, so I hope your parents are able to see that not treating an animal with an obvious medical issue is pretty irresponsible.
Finally, is your pig eating? Ill or with pain, guinea pigs may go off their food. Weigh and observe your pig to see that he is eating/eliminating normally. A guinea pig that is not eating is an emergency. They are constant grazers by nature, going off their food can lead to death from bloat or gastrointestinal stoppage. There are stickies on the page about syringe-feeding and supplementing a pig who has stopped eating, so I would go over those to have the info handy in case it's needed.
Really, a vet visit is warranted here, and I hope that is able to happen for your pig! Best of luck to you!
