I definitely agree with all the advice already!
I have 4 kids, spaced 20 months, 20 months, then just less than 2 years. We took the older kids to prenatal visits, talked about babies, included them in choices. We had them visit the new baby as soon as possible after the birth--my oldest daughter (who was then 5) actually witnessed the birth of our youngest son--she was given a disposable black & white camera to take pictures, and had the job of announcing the gender of the baby.
We let the kids hold the baby--sitting on the couch with a Boppy pillow on their lap. Once we had two girls and then started adding boys, we actually had to set a "sharing timer" for the girls to take turns holding the babies because they liked that so much. But you need to stay close by for this--with each of our sons my younger daughter at one point heard the doorbell ring, knew it was Nana & PopPop, so she slithered out from under the baby/Boppy to run to the door--and I caught the baby just in time to prevent injury.
You will be surprised at how well your DD adapts...and the best thing will be as you see her mimicing you as she nurtures her new sibling. Good luck!