Rebecca, you are NOT a bad person or a bad owner. Don't put this idea into your head. The fact is that you are a genuine girl who thinks that when the events go bad the adults are there with their money ready. The truth is different... many adults don't care of many things which are important for us (a piggie and his/her health for example); many adults see your piggie as a "piggie" which costs 10€ at the shop and it sounds absurd to pay a fortune at the vet...Yes, I feel like the worst person /: I never saw this coming and never thought ab it, but as i said above I'm gonna now on save money incase. I will do whatever I can do for now on, and she's eating tho and i'm gonna make sure she somehow eats more and give her more vegetables. I'm keeping an eye on her.
And you, as a daughter, cannot do much. But maybe something can be done: ask your Grandparents if you have any; ask your parents about paying in advance your next birthday present/christmas present/party/pocket money/mobile's card (you can turn the mobile off, it is not necessary and I also live mobile free); you can call a vet in front of your parents and explain him the situation... maybe your parents will not like the poor figure or maybe the vet will sign for you some prescription.
Another thing you can do is explaining your parents (I am not sure they know this point) that your pet is not only a common piggie, but is the piggie you love... and if she dies without a vet you will suffer a lot...
And for the future, before adopting a pet, before homing a pet into a FAMILY, remember that a pet or a child or a guest or a plant is not YOURS, but it belongs to the whole family. If only one member of the family disagrees the presence of the VET or wants to be far from troubles (and also plants need expensive cares sometimes), it is better living pets free and this is what I have written in another thread and I will go on writing and saying this aloud.