Do you think im right in this feud?

My advice would be don't let her actions affect how you act. Your husband's little sister is just young and immature and maybe lazy. She's just a teenager and probably doesn't have much going for her at the moment. You're married with a child. Be the adult and Invite her over sometimes, not just when you need help because she's not a slave! Act nicely towards her and encourage her, you might make a good impression on her and then there is no reason she would say anything bad about you. As for the baby shower, she probably won't want to go if she doesn't like babies so she's not going to be happy about it - try to respect that and don't push it. Take it easy and don't be drawn into an argument with her about anything. Set a good example.