Congratulations! My boys are 20 months apart- one is 2 and the other is 4 months. I read the books, talked about Jonah and how he is in my belly and will come out and he'll be a little baby in our family, etc. All these things are great to give your child an idea of what is to come. HOWEVER, my son is very smart for his age too, and communicates well, but the concept of a baby in the FAMILY is too foreign for any child that small to understand until the baby gets there. Basically, you just have to meet your big kid's individual needs while she gets used to the baby being around all the time. The first several days, my older son would not call the baby "Jonah", because that's the name he associated with my belly, not this new baby : ) He kept his distance for a couple of days, but he'd come look at him or watch us taking care of him. When Jonah was 3 days old, Jonah sneezed and Isaac laughed. After that Isaac started calling him by his name and talking to him, and gradually grew more and more interested. Now if I ever take Isaac somewhere without Jonah, or even if they're in separate rooms, he asks over and over where he is, and acts really sad. Basically, what I'm saying is, the books and all the other advice is great (and definitely keep reading them after baby gets here to solidify the concept), but your kids will bond on their own and in their own time. I will tell you one thing that worked wonderfully for us was not to say, "Isaac, look at your cute baby brother", like all the visitors would say. We started holding the baby up and saying "Jonah look at your big brother! He's --dancing,playing with cars,etc.--" This made Isacc feel proud and made him feel like Jonah loves him too, which he does! Jonah still laughs hardest at his big brother being silly...Don't stress, they will figure eachother out with your gentle guidance!
P.S. I had homebirths, so Isaac came home from Grann's as soon as the baby got here- just trying to give you an idea that Isaac was around Jonah constantly for three days before he started to come around. Just don't want you to be discouraged if your little girl isn't attached to the new baby by the time you come home from the hospital...