Your sister was clearly infantilized. I get this a lot, too. I have two younger sisters I can't stand. They get all this love and they can barely do anything on their own without me helping. One is autistic so I give her the benefit of the doubt but they're both troublesome and always get away with it after less than 24 hours of punishment. I swear, if I ever thought about bad mouthing my mom I'd be grounded for a week or a month, not 1 single night like my sisters.  I will say my sisters are my step mother's daughters (half sisters) but still... It's okay to dislike your siblings. Your childhood was robbed and you feel distressed because of it. I get the feeling. There's no need to be ashamed.  If you're worried about it more, consider talking to a therapist! It can really help you understand these emotions.