I think if it was me that ws putting on the shower I would do the following:
1.) get some invites that have the princess motif on them..I am not sure what you have to work with...if you are lucky enough to have a Cricut that would be perfect...you can make them exactly what you want them to be...if not look on line...I would also state on the invite that this is a Princess Baby Shower...here is an idea at this website:
Photo Baby Shower Invitations - Royal Welcome: Daiquiri by Tiny Prints
2.) order from say someplace like a large grocery chain that does Birthday cake...I believe if you have a Walmart around they do them...get them to do one of the Princess castles...have them put the Disney Princesses on the castle along with a couple of baby carriages...colors should be pink and white...then on the side have them do up some cupcakes with pink frosting and some tiny princess tiaras...
3.) As far as food goes, I would continue the theme of pink with the food...you can use food coloring to do alot of this...You can dye alot of your dips just by adding a little red food coloring...just enough to tint pink......add to frosting on other items you are having...
4.) You can play games from this site or a form of:
Princess Party Games - LoveToKnow Party
5.) Then when it comes to the gifts, because you have let the people know that the party has a Princess theme, they should bring items decorated in Princess themed paper and ribbon...take the ribbons from each of the packages and attach them to an adult tiara that is then worn by the mother to be...
6.) I think that to make the party even more fun and make each woman invited a little gift bag as a Thank you, just a small bag of Princess themed items that can be picked up at the Dollar store(these could also be used as the prizes for the games)
I hope this has helped a little...and if the others can not get on board...have your own and let them have theirs...just make sure you invite them...your decorations should follow the theme, as in pink crepe paper etc...