Do you have a syringe? If not a teaspoon will do, but you can mash up her pellet food into a powder and mix it with water, this can then be syringed into her mouth a tiny bit at a time, or offered on a spoon for her to try to eat for herself, if she is too weak to swallow then stop as she will choke and thats a pretty good sign that she's likely to pass away. If she chews and swallows, good sign, keep trying to get food into her little and often, you can puree some vegetables high in vitamin C which will be useful, bell peppers are a good one to try.
A small plastic bottle filled with warm water inside a sock placed next to her will help keep her warm, but not hot. Also offer plain water as well to keep her hydrated. If you can get her guts working again and build her strength up she might come round, or make it long enough for your parents to hopefully change their mind about seeing a vet. If not this will at least keep her somewhat comfortable.