I wouldn’t focus to much about the possibility of boy or girl, but talk in terms of the baby (neutral) and how sweet it will be. Once it’s there, I’m sure the sex of the baby won’t be making much difference !

Find some books about having a baby/little brother. Read them to her a lot.

She doesn’t have to be excited. Just explain to her that its not something you get to choose and its ok if she feels sad if it tutns out to be a brother instead of a sister.

I would take her to choose a present for the baby from her. Also get her to help you decorate his room (if it is a boy). My daughter wanted a sister not a brother, however she loves him and wouldnt change it now, I got her to help with everything and it helped.

Perhaps get her involved in shopping for stuff for him or even getting her her own boy doll.