P.,
Your idea is beautiful and very conscious of the impact a new baby will have on Kaitlen. My only suggestion is that it would be even better to do it BEFORE your baby is born! Why?
1) The excitement of the new baby will be in full swing and Kaitlin will have already picked up on being "less important" by the time you are able to have a party for her.
2) You will be recovering from a birth--and there are never any guarantees that you will be energetic, or that the new baby will let you sleep, etc. Just the way it was impossible to understand what it would be like to give birth before you actually did it with Kaitlen, it is ALSO impossible to really realize what having the second one with an older child will mean. It takes a lot out of you at first!
3) If you have the Big Sister Party BEFORE the birth, you can incorporate more easily the idea of how very important she is, and the way the whole family circle is now going to "open up" for a whole new person. It's much easier than trying to help her with the concept after the fact.
With that said, I had a special "blessing way" (a Native American style ceremony) for my daughters, as well as one for myself, with each new pregnancy. Here are some of the things we did...
-I invited the women who have been important in my daughter's lives, as well as their father and one special friend their age.
-We each brought a special candle for my daughters, said something special about them that we wanted to wish them as they helped me give birth to their baby sister, and placed the candles in a large bowl of sand. The candles were lit during my labor, as a reminder for them of how important everyone thought they were.
-We each wrote something about what a great sister they would be in a tiny little book I got, and they got to keep the book in a special place.
-Small gifts were given.
-We walked them up some steps, to symbolize that they were moving to a new, higher place in the family.
I want to send my blessings to you and your family. With so much thoughtfulness, you must be a wonderful mom!