I don't want to help pay for my sister's baby shower
Why do you think that that is not your job?
I cannot give any sensible reason, but I somehow hate her for having sex before marriage. It is wrong.
It's good to help out your sister with her baby shower. You shouldn't let your personal feelings get in the way of helping others.
No, fuck that...
I think that that is what sisters are for. You should help your family out when it comes to expenses like this.