K.D.
In my opinion this is totally normal and will change over time. All 3 of my kids did this and my 18 month old still has a fit if I hold another baby. When my oldest was 2 years and 3 months old I had my 2nd baby. For 2 weeks it was rough and you could see how this new family member had an effect on my son's behavior. After that though, he was totally fine and life was completely happy. When my 3rd child was born I thought that my little girl would have the hardest time since she was currently the "baby" and my oldest had already gone through welcoming a new baby into the house. Quite opposite; my daughter was great and never had any issues, but again, my son who was then 5 years old had another couple of weeks of hard adjusting. Your little girl will be great and love her new baby, of that I'm sure. Maybe you will go through that rough adjusting period and you might notice her behavior to be not the best, or maybe you won't and it will ne fine from the start! But don't stress anymore over that because all will be fine.:) Good luck to you!