Are you saying that the plan is to put your daughter back into the custody of her birth mom? Having had lots of experience in custody cases I'm wanting to address all sorts of issue. But I'll let go. LOL
As to regressing this is very normal and not problematic. Your daughter needs to go thru this in order to heal. I adopted my daughter after having her as a foster child. At 7 she became like a preschooler in many ways some of the time. The advice given to me by therapists was to, as Ephie said, to meet her where she's at. I put on and tied her shoes and helped her dress at times. I allowed her to talk in a little girl voice part of the time. I did encourage her to talk in a big girl voice just as I would've when she was a preschooler. I treated her as I would at the regressed age and treated her at her chronological age when she acted that way. Just as I would with a kid not going thru this I encouraged growth. I really relied a lot on her therapist to know what was best to do.
This is a big adjustment for both of you. Try to relax and let happen what happens. Try not to search for ways this is problematic. I kept a journal which I shared with my foster daughter's caseworker and left it up to the caseworker to decide what was working and what wasn't unless it wasn't working for me. In that case I talked with the caseworker and the therapist.
Your daughter needs to know that visiting her birth mother is alright with you. She should feel no judgment, criticism, or anxiety from you. Hard to do I know, especially if it's possible that you'll lose her. And it is difficult to share a child with another mother. I had frequent contact with my foster daughter's birth mother as well as some members of her family.
I adopted my foster daughter when she was 12 or so. I encouraged her to maintain contact with birth family who supported me. I, first spent time with birth family so that I knew how they felt about me and saw that they were supportive of the adoption.
Your daughter's birth mother is an essential part of her life even if she ends up not being with her. You are setting the stage now for her future happy life. Keep in mind that even if this woman is less than responsible that she is a part of your daughter and always will be. Your daughter must never hear you criticize her.
In my situation, when my foster daughter asked why she couldn't live with her mother I said because the courts have decided that she can't take good care of you. Tell the facts in a neutral way. I know you didn't ask that. This is such an important topic for me.
If your daughter becomes agitated and angry then it's past time to get her in to see a child therapist. Depending on the circumstances, now might be a good time to ask about doing this.
Listen well to Ephie's post. She is taking care of her sister's daughter and has had experience in this area. She is one smart woman.
Note: I read your previous post. I very much empathize with you. I went thru something similar, emotion wise, with my daughter. It was nearly 3 years before they terminated her birth mother's parental rights.
You mentioned going in front of a judge and jury. I doubt very much there will be a jury involved. Custody matters are handled in family court. Just like there is not a jury in divorce cases there isn't one in custody cases. I suggest, that unless your attorney is experienced with the assigned judge and suggests you don't go in front of the judge, that the judge is a safe person to trust in making a decision. I do think that in your circumstances it looks better for you to have made the decision you made. You are showing by that decision that you are acting in the best interest of your daughter.
With my daughter we went in front of 2-3 different judges over the years and I found them all to be compassionate and fair. They do have hoops that they have to be sure that the case goes thru but in the end, if everyone's done their job, it's likely that the decision will be in the child's best interest.
If you haven't already, I suggest getting a guardian ad litum assigned to your daughter. My daughter's lawyer advocated for her return to her birth mother because that is what my daughter said she wanted. He did not consider her best interests. He was also very inexperienced. He refused to talk with me at all. It sounds like perhaps your daughter's attorney believes that being with the birth mother is automatically in her best interest. A guardian ad litem is experienced in such cases and will add a different dimension to the decision.
Please write to me if you have further questions.