I know you've probably guessed this already, but never leave your pig outdoors unattended. I really don't want to make you feel worse than you already do, but please, never let your pig be outside without constant supervision because things like this happen.
It's likely after being attacked your girl is in shock, which can be extremely dangerous for such small animals. That would explain her trembling and refusing to eat; she feels VERY vulnerable right now.
Get some saline solution if you have some in, soak a clean cloth in it that hasn't been washed with anything perfumed, and gently stroke the wound with it to clean the area. No paper towels as they may disintegrate and get stuck to her cut. If you have no saline solution, clean it off with tepid water.
Following that, get her to a vet. If you can't get her to a vet for whatever reason, seek telephone advice off a 24 hour surgery until you can get her there, but if possible, have her seen immediately.
Keep her as comfortable as possible and hand feed her hay every 30 minutes if she'll eat it. If not, try a favourite veg just to keep her digestive system active.
Do you have a syringe? If possible, give her a small amount of water every 30 minutes also to avoid dehydration. If you have no syringe, cucumber provides plenty of hydration as well.
She may be infected following a wild rat bite, so try and keep her quarantined from any other pigs you have to be on the safe side until she's been seen by a vet.
I hope she's okay