Getting aniexty from foster child.

So right off the bat I just want to say these are my neices, but they are my nieces that I haven't seen since they were babies because me and my sister had a falling out years ago. So I decided I was going to do kinship care for them with the intent to adopt. We have had them for 3 months now. The one we were told had the most "problems" is doing amazing in school, here, with our bio children and in social settings. (They are 11 and 12 by the way). The older one who we were told was the sweetest and most respectful isn't doing too well. I feel like a horrible person saying this buy she gives me really bad aniexty. She cries if she doesn't get her way like a toddler. We were told she had absolutely no problems. She is overly clingy like to the point I have to go pick myself in a room and listen to her knocking or sitting outside of it for extended amounts of time. She follows me from room to room and just stands there looking at me. If I leave to go to the store she asks my husband a million times when I am coming home. Homework is impossible. I think her old foster parents use to just do the homework for her because I will sit with her working on it and if I don't tell her what to write or what the answer is she will just sit there and cry. She gets super jealous if me and one of the other children even look like we are having a good time. I have talked to her therapist, mine, and the family therapist about it but I don't think they understand the extent of how bad it is. I have been having nightmares about me and one of the children having a fun day and her killing them because she was jealous. This is a horrible feeling because I want soo badly to connect with her but I can't if she gives me aniexty. I completely get the reason why she is clingy. I feel sad by what they have gone through and want to be there for her. She knows how I feel about her following me and about needing space but she doesn't really care that I want or need space. Anyone gone through the same thing or have any advice? We have tried reward jars, therapy, me and her having a time during the week that is just hers. None of it seems to be working.