Get her involved in whatever way you can.
The doll idea is ab great one.
When DS2 was born, DS1 wasn't quite 21 months. We had a box of toys that we brought out only when I was feeding DS2. There were his fave toys and a cpouple of books. That definitely softened the blow of some my time being taken up by another baby. When I finished feeding, I would distract DS1 and put them away or let him play with them til a convenient time, like lunchtime.
I agree with a previous comment about letting your DD touch the baby (Obv if she is poking the baby's eyes or pushing the fontanelle, DS1's fave tricks, then intervene) Your DD will be fascinated by the baby, so let her explore! Babies are v robust. Just emphasise they you need to be gentle with abaies because they are so little. Encouirage her to stroke the baby's hair etc etc etc
If shge regressews a bit (Like wanting you to spoon feed her etc) just ride it out. It will pass. DS1 has a pahase of wanting to be cradled like a baby about 2 or 3 months ago, I just let him carry on. I also used to find it helped a bit to emphasise all the things DS1 coyuld do that abaies coyuldn't like walking, feeding himself etyc etc, but don;t make too much of "you are a big girl" because she is still a baby herself! I think I expected too much of DS1 in terms aif behaviour etc after U hgad DS2 because he seemed so grown up all of a sufdden. I kept haing to remind myself that he was still very young!
Finally, GET OUT OF THE HOUSE EVERY DAY! Take your daugeter to the park and wear her out. Get a double buggy and go for 2 walks a day. I did this when DS2 was tiny, and it kept me sane.
It really isn't as bad as you think it's goingt to be, I promise. You will find your own way, and you DD will be a great big sister.