Maybe she feels jealous that her siblings get to have both of their bio-parents under one roof, and she does not. She might feel jealous that your child will get to see DH every day, and she does not. She might feel jealous that her little sister gets to see her biological dad every day, and she does not.

Maybe DH could spend some one-on-one time with her every now and then and make this a permanent practice that remains in place after the baby is born. Maybe he could call her every day. Even though a phone call isn't the same as seeing him, it might help to at least decrease the jealousy, as would one-on-one time with DH.

Also, DH should keep in touch with the school therapist and see what she recommends, and follow through with her recommendations.

exsd took to bd3 well the first day we brought her home from the nicu. starting from day 2 on until we split, she made it clear she didnt like being 1 of 2 kids her daddy loves.

the funny thing was, when i was at school or a friends home and exbf was left to tend to the kids, exsd was a "big help' and showed she really loved her half-sister. at first i thought he was covering for her as usual. but quite a few times friends or family had to watch the kids for various reasons, and all had said the same thing! so in conclusion, exsd was being seriously mean and sneaky with bd3 only while i was home--when i wasnt she changed.

in the beginning, we made exsd part of everything related to bd. from letting her help open gifts at the babyshower (and giving her a 'big sis gift and hat') to fighting with nicu nurses to let her come in and see her sister, we did what we could to make her feel like there was no 'half' about it--it was her 'sister'. after about a year of her STILL playing victim, we both said enough already and basically made life normal, no more overcompensating the exsd. we didnt leave exsd out of things, we just didnt baby HER to help her adjust.

DH and I don't have any kids yet but SD10 has two younger half-sisters from her mom. I'm not going to lie, she doesn't really care for them too much. She complains about them all the time and doesn't play with them very well. BM called DH a few weeks ago and said she was worried that SD was depressed because she spent the day there crying in her room and wouldn't play with her sisters.

Again, I'm on the outside looking in here, but I think the main issue is that BM forces SD to "bond" with her sisters. She makes SD come over even when BM's not going to be there because she "has to spend time with her sisters." She forces SD to share her clothes and things like that with her sisters because she wants them to all get along. I'm all for sharing but I do think that kids should be aloud some of their own things. I think because of this SD looks at spending time with her sisters as something that she has to do as opposed to something that she wants to do. It's like a chore to her. So my advice would be not to force it on her. Don't try to get her to love her sibling, just let it come naturally (even if it takes a while to catch on). It's kind of the same advice we get as step-parents meeting the step-kids....don't force yourself into their lives, just be open and let them come to you. I would follow that same logic with a new baby. Good luck!

DH and I do have children together. When I was pregnant with our first, it was horrible. SD was only 4 and at that point in our relationship, she didn't like me much(her mother said alot of negative things to her and in front of her about me). SD 4 refused to acknowledge that her Daddy was having another baby. She refused to touch my belly when BD would roll and move. And to make matters worse, BM came to DH's house(before we were married/living together) to "check in" and found all of our sonogram pictures of BD spread out on his kitchen table. She flipped out. She told SD4, 5 minutes before taking her into preschool the next morning that "Daddy is having another baby and he won't love you as much" This really hurt SD4. I think BM was hoping that my DH would feel sorry for BM, in some weird way. Long story short, our BD is now 4 and SD is now 8. They have a wonderful sister/friendship now. And now we also have a little boy of our own who is 1. Both SD8 and BD4 love him dearly.
But, I must add. SD, 4 at the time did have a really hard time adjusting. I could see she was soooo jealous. My DH just told her straight up that this is her new baby sister, she's not going anywhere-ever- and it is something that you will have to learn to accept. It took SD quite awhile to fully adjust.

I don't know if me sharing my experience helped.
But, I hope everything works out for the best for you

~Never interrupt your enemy when she is making a mistake.~

~No-one can make you feel inferior without your consent.~