Even at age 2 changing the date will not be a big issue, your little princess will not know the difference but changing or not the day, just keep it sweet and simple, with mostly family, the fact that is HER day, with her cake and her gifts, people around celebrating her with a nice special dress will maker her super happy.
Some one suggested pizza, that is always great help, do not cook and do not worry, let your mom, MIL and SIL handle the work.
If you want to be involved, before you deliver make yourself or buy party favors, if there are going to be mostly grown ups with few kids ( I would keep the kids number limited) buy special Themed cookies (being princess cookies, shaped as 2, or birthdaycake shape cookies and put them in a clear bag with a nice ribbon and even a small (home made) tag with your girls name.
If money is not a big issue, order some home delivered balloons and make sure that she goes to the door to receive her special delivery.
Since the little baby must have or will be receiving a lot of new stuff, get your little girl a lot of gifts, they do not have to be expensive, just a lot, and before your baby is here... wrap them all in beautiful paper and do not forget the ribbons.
now the tips of where to get stuff... I love etsy, I bought for my daughter last year hello kitty cookies as party favors for everybody... I also got a paper made cake topper with hello kitty and my girl's name. Y got at Target little toys and put them in clear bags and printed myself some hello kitty personalized tags.
Balloons, balloons always set the party mood and make the kids super happy, you can buy either at target, walmart or party city the package that includes de tank and balloons and they can be inflated at the house or you can order them in advance at party city and have someone pick them up.
For my daughter's 2nd birthday the theme was butterflies, the party favors I made were soap shaped as butterflies and dragonflies, I got the molds and materials at Michael's, they are super easy to do and they looked beautiful (and cheap) again in clear bags and a nice personalized tag. That year I got at Etsy.com some edible butterflies and decorated a simple cake with them. It looked beautiful.
I love birthdays, if you want more ideas and where or how to get some of this stuff just send me a personal message.
Good luck, congratulations!!!