Hi E.!
I've been in this position, but with my step-daughter. She was "the princess" for years and received the most attention because of her creativity and zest for life, not to mention how beautiful she is.
Then.....along came a baby boy! Yes, she would "fight" to see if we would choose her over the baby, when it was obvious that the baby was screaming and needed my attention.
This is tough, let me tell you, because what can easily happen is resentment. Your daughter can easily begin to resent your new baby, and feel "hate" toward him for "ruining" her perfectly good life!
I had to try to NEVER interrupt her to go get me a diaper, because then it would "set her off". I'm sure you know what I mean. So, then I thought, I cannot do this for the next 10 years, I have got to try something!
I decided to have a "party" for her. I allowed her to invite about 6 of her friends. The party was a "Now I'm a Big Sister" Party. Every friend had to dress like a mom going out to a fancy party (That was fun in itself to see how these girls think their mom's dress). I set a "fancy" table with champagne glasses and all. I tried to make it as fancy as I could, and as decorated as I could.
All the games were like Baby Shower Games, except I tried to "target" the work a new mom has to deal with. Like multi-tasking, who can Microwave a bottle, get a glass of Lemonade, and take out the "Lasagna" the fastest? Time them so they can see how fast they can multi-task :o) The winner gets a prize. Another game was a SMELLY DIAPER game. I bought small candy bars, and microwaved each one in a baby diaper until it melted. Then I smushed them really good! I numbered each one with a Sharpie and they had to guess which candy bar was in the diapers :o) Funny game.
Anyway, after the party, we went on with our "normal" life. I still tried to be sensitive to her, as I always was. It was HER that had come around a little. It was actually amazing. By the time our son was 2, she was a VERY proud big sister, and very helpful.
It really is just climbing over this "first hill" with her. There are alot of emotions she's dealing with. Maybe it's time to celebrate HER. If you have photos of HER when she was an infant, it would be nice to share them with her. Talk about her Shower, and the things she would do as a baby. It might help, too.
Good Luck, E.. You're in a sensitive spot. I wish you the best with your little family.
Love, N.