Stepchildren and New Baby

Long post alert. I’m desperately searching for advice and support.

My husband and I are expecting a baby. We’ve been together for almost 5 years and married for 4 months. He has two girls from his first marriage (17 & 14) that he’s had full custody of since his divorce 10 years ago. His divorce was very difficult and the year leading up to him filing was also very difficult. His wife became an alcoholic. He tried everything he could to get her help, but nothing worked. She became mentally and physically abusive to him and mentally abusive to the oldest. She became dangerous for her children to be around her and she tried everything she could to make his life miserable.

Now, I’ve been helping to raise his children, who I consider my own, since they were 9 and 13. I have great relationships with both girls. We told them a few weeks ago we were expecting and they would have a little sister. The oldest is very excited. The youngest became irritable and began to cry shortly after being told. She says she doesn’t want to be the middle child (even though she has a younger brother from her mother she doesn’t see), she doesn’t want another sibling, and she feels her sister is the favorite and now the new baby will be the favorite. It's like I try to talk to her about it and she doesn’t want to talk about it, she wants nothing to do with the baby, she doesn’t know if she’ll like her or not when she’s born, and what's the point of her even liking the baby because it won’t remember her anyways.

I know she’s young and still processing this life changing event, but I can’t help feel worried for the new baby. Not in the sense she’s ever do anything to her, but that she’ll be mean to her. Her father says her feelings are coming from a place of her repressed traumatic childhood feelings because of her mother. That may be true to a certain extent, but I’m just worried. It just really upsets me to think that my baby could potentially grow up being disliked by one of her sisters because she didn’t want her here.

Does anyone have any type of similar situation?