Hello A.!
I have a 3 year old son, and a 11 month old daughter. My son was 2 years old when I going to have my daughter. The way I transitioned him in accepting our new arrival was by telling him early on in my pregnancy that he was going to be a big brother. I used pictures in books to explain what a big brother was, I also showed him other kids that we passed in stores or saw on television.
To make my son feel special and happy about our new arrival, I ensured him that he is going to be my big helper, and I made it know to everyone; family, friends, co-workers when my son was around me and those individual's started talkiing about baby. When ever baby was mentioned and my son was around, I make sure that my son had some kind of involment in the whole baby talk. (to be totally honest, I think he got a little annoyed by me mentioning him so much)I always made it appear to be about my son.
Even when my daughter was born, (because newborns don't become aware of how much attention they are actually gettiing, plus they sleep ALOT, I put all my attention towards my son, and when my daughter did wake up, my son was there to help hand me diaper ect.
So make it about your daughter, and bring your daugter into everything you do with your newborn. Tell her how she is going to be your big helper, and when people mention baby, include your daugther and let her hear you say the great things your daugther and what she is going to do to help with baby. Then when baby does come let be there to help you change her and show her how the newborn is her younger sister and how she needs to protect her and her safe. Then when the time comes when your newborn gets older your attention towards both of them well ease so naturally and equally for both of them, not even they will realize it. I really hope this helps. Good luck with your labor, and your current situation.
K.