Am I wrong??

Ok so I had asked my sister to plan my baby shower right after I found out I was pregnant. (21 weeks now) Shortly after I asked her to include my SO sister I the planning. Meaning just ask her for a little input. Well now she is saying that if I want someone else to help them they can just plan it and she will just sit there and attend like she isn't even my sister!! She says it's her birth right to throw he baby shower and me asking her to include someone else is rude. My sister also just moved like 8 hours away and is low on money. So I figure asking his sis to help would be a good thing. But she is turning it to where it's all about her and not the celebration of my first child. Am I wrong to have wanted her to include someone else? Am I being selfish?