do you have an Idea of what other animals would get along with a rabbit?Never let a piggie interact or be in close contact with a rabbit.
Each species can carry a disease that is harmful to the other species. For example, rabbits can be carriers of the Pasteurella bacteria without having or showing any symptoms. Guinea pigs are much more susceptible to this bacteria and could die from it. This reason alone seems enough to keep the species apart.
It's also true that an inadvertent/accidental kick from a rabbit could cause serious harm to a piggie -- regardless of the size of the rabbit. We saw this happen with a forum member years back. She disregarded the advice here to keep her piggie away from her rabbit because "they got along so well." She frequently let them have playtime together... until one day, the rabbit just hopped up and happened to kick out its back legs. The piggie ended up with a few broken ribs and internal injuries!
When we had both piggies and rabbits, we kept the piggies in a raised C&C cage so they could never come in contact with the rabbits.
Do you and your sister share a room? If so, I would suggest keeping whatever pet(s) your sister gets away from the rabbits. Some dogs and some cats may develop a friendly relationship with rabbits, but that's only on a case by case basis (and dogs or cats are typically "family" pets. It sounds like your sister is wanting a pet "of her own."do you have an Idea of what other animals would get along with a rabbit?