Sadly, this very normal and to be expected. It just really doesn't matter if she has a little sibling in another home in a different family dynamic...she needs to know she isn't being replace with YOU with DADDY.
Think in terms of this child. Her world is a ping pong game. She is seven, not well equipped to understand all the ins and outs of the adult world and all the good "intentions" and inevitable consequences which may not benefit her favorably but works oh so wonderfully for the big people controlling her world. It really isn't fair, she doesn't have a "home" or a "family" she has part-time and NO ONE to share this reality with because she's the only child in her familial double dynamic, so be patient with her.
Hug her a LOT. Tell her how lucky or blessed you are to have her. Express excitement at HER being a big sister and how lucky/blessed this baby is to have her to show her the ropes. Have her talk to your baby, have her feel your baby, have her call this her baby...to begin her emotional bond with this baby.
Avoid becoming agry and impatient with her, after all, she did NOT ask for this craziness no matter how fun and loving it can and may be. Staying sweet and loving to her will reduce her demand for time and affection.
As you've said before, she's gone through this whole new baby thing with a step-parent. Perhaps the step in her other "home" didn't handle the transition so well, as is so common, because that little baby is the step parent's "REAL" child and she was just the kid that came with package of mom. Perhaps she's afraid, you, too, will forget how wonderful she is when you hold YOUR "real" child.
She's going to want to hold the baby, be brave and allow her to while she sits beside you. She's going to want to be around when you're feeding the baby--this right here will be a big thing because if you're breastfeeding, chances are, you're not going to want her around feeling self-conscience.
Create a routine in your home centered around HER with the baby. Talk to her about helping with the baby, the diapers, the singing, the holding, the loving... When you're nursing your baby, have her get you some books that you can read to her while you sit closely together. Color with her. Draw with her. Do her hair. Let her brush yours.
Instill in your husband the VERY important need for him to tend to HER while you're bonding with your baby and doing things alone--like nursing if you intend to hide that from her. This can be a very, very important time of rebonding and closeness for her and daddy that you'll will benefit and be grateful for.
If she's reverting she's letting you knowthat she needs extra care...give it to her and you'll see things move smoother.
Keep Her perspective in mind and you'll know exactly what to do...there's hope.