There seem to be quite a few different things that can cause this very alarming situation and I'm so sorry this has happened to you. Some are relatively simple to resolve and some are more difficult to treat and sometimes no obvious reason can be found. This is why a vet visit is so important - we can't know what is causing it and it's tempting for the owner to think, "well, I'll just try giving this vitamin or this food supplement and see if it makes any difference" but this can sometimes do more harm than good if they are OD'd on a supplement and if a vet visit is delayed while we wait and hope for any change.
Only a vet who gets hands-on with your piggy has a chance of being able to pinpoint the reason straight away, or at least rule out what it's not, and they will outline the correct treatment. There are reported cases of paralysis like this where the piggies can get completely better - your girl has youth on her side and it seems some movement is there so treat her gently if you move her about and make sure she is still able to eat and drink.
I had an older girl who suddenly lost the use of the back legs but her loss was absolutely complete and quite likely the result of rough handling or dropping in her earlier life before she 'retired' to my house. She dragged herself around using her front legs and I made sure she had a comfortable and absorbent surface and that food, hay and especially her drink bottle/bowl were in easy reach. She wasn't in pain - she couldn't feel anything in her back legs. You might have to offer your girl mushed up food in a syringe if she is struggling to eat - if you can't get any of the finally ground recovery mixes (like Critical care etc) you can soak some of her normal pellet food in water to soften it to a mush (personally I grind mine up dry and then add the water). Make sure everything is within easy reach for her and keep an eye to make sure she is not lying in her own pees or poops. Monitor her poops to make sure she is still producing the same amount and they look normal. This could be something she gets over quickly with treatment but if she stops eating/drinking the battle may be lost before she gets a chance to recover. Good luck with the vet appt and pls keep us updated, we'll be thinking about you x