I hate the way my sister treats my pets?

i have a little kitten and my sister has always been rough with animals. her own cat was horrible and scratched everybody. she picks the cat up with one hand and holds her up in the air while she squirms and hollers to get down. she also flicks the cat in the face and hits her or roughly tosses her to the ground if she is doing something my sis doesn't like. she won't listen to me when i tell her to stop either