I am so sorry your going through this, it isn't payback for getting a piggy from a breeder, it's just bad luck.
Like someone has said you are not to blame in anyway. This must be the worst time for you, all I can do is to be so sorry for the way you've been treated. I've been lucky that mine have never had a URI. Regarding your the small claims court you would have to enquiry about that. I know it is different, but I had a faulty bed & I had to go into mediation because you can't go to the court until that's been sorted. With all the hoops you have to jump, it can be well over a year. Do what the RSPCA say & claim vet fees off, of them.
If you have given your name & phone no they have to let you know what happens.
If you want to let off steam we're here. All the best for your piggy with a piggy slave like you, she'll be fine.