It sounds like this is more than a shower? Its a shower and a party, right? I wouldn't be bothered in the least by it.
First off, I have never understood the whole "only those invited to the wedding should be invited to the shower" thing. A lot of people have very small weddings--family only or get married at a distant location, but have a lot of friends that would like to celebrate with and honor the bride at a shower. Same thing with the bachelorette party.
If you want to go and celebrate with her---go. If you don't, don't go. But there is certainly no sense in getting all bothered by it. And certainly no sense in calling anyone rude and uncaring (not you OP).