baby shower???

First off I would like to state that I believe baby showers are a wonderful thing! Babies are cause for celebration and I believe all mothers deserve the most support when a baby is coming into this world. If seen as acceptable I would enjoy baby showers for every child not just a mothers 1st. Most aren't comfortable with this so I end up having a small get 2gether with the closest friends & celebrate the mother2b that way. Anyways my question is about my sister. She is due march 25 and hasn't been the most excited about her 1st pregnancy. She didn't formally tell every1 that feels they should have been told that she is pregnant. Right or wrong I don't really have an opinion. But as she is getting further along she is getting more & more comfortable w/the whole thing& at times even excited. The problem is that I am about to begin planning a baby shower for her & have been told by more than 1 person that she or I can't expect people to bring her gifts when she hasn't even thought enough of these people 2 formally tell them she is pregnant. I say screw those people... if they can't put that aside & come celebrate a life about to come into the world I/don't want them there anyways. What do u think? How should I approach these people as I send out invites?